Common Topics in
Roadway Defect Cases

John C. Glennon, D. Engr., P.E.
January 2003 (copyright)

Because of the repeal of the sovereign immunity statutes in most states over the last 25 years, roadway defect tort claims have mounted in the United States. The most common categories of tort litigation are roadside hazards, sight obstructions, pavement edge drops, construction and maintenance work zones, and rail-highway grade crossings. These categories are of major concern not only because of the number of claims, but also because of the number of claims involving life-adjusting injury or death.

Although many authoritative technical documents are used to prove or disprove negligence in roadway tort claim cases, the following seven key documents are used extensively for this purpose:
  • Manual on Uniform Traffic Control Devices1

  • A Policy on Geometric Design of Highways and Streets2

  • Roadside Design Guide3

  • Railroad -Highway Grade Crossing Handbook4

  • Traffic Control Devices Handbook5

  • AASHTO Maintenance Manual6

  • Traffic Engineering Handbook7

These documents give the majority of specificity to roadway design, maintenance, and traffic control principles and standards.


Prior to 1965, the prevailing philosophy in the roadway community was that drivers who ran off the road were somehow deficient and deserved the consequences of their imprudence. In the late 1960's, as the evidence began to mount that almost 40% of all fatal accidents involved single vehicles running off the road, the prevailing thinking began to change and the forgiving roadside philosophy was born. This philosophy recognized that drivers run off the road for many and varied reasons, and it was the duty of roadway agencies to design roadsides to minimize the severity of these roadside excursions.

As this new philosophy gained favor, the clear zone concept emerged and large-scale efforts were launched to clear the roadside environment, particularly on Interstate highways. Foreslopes have been flattened, breakaway signs and lightpoles are now almost universal, and guardrails have been installed on steep slopes and at large fixed objects close to the road. The current clear-zone standards are presented in the Roadside Design Guide.

The prevailing roadside hazards today are most noticeable on non-interstate roadways. Some hazards are remnants of past folly, neglect, or indifference. Typically large trees, steep slopes, culvert headwalls, bridgerails, and utility poles can still be found very close to the traveled way on thousands of miles of two-lane roadways. Then too, many guardrails of the past have too few posts, have too low of a beam height, are too short, do not completely protect against the hazard they are shielding, or have non-crashworthy end treatments.

Steep slopes, faulty guardrails, or fixed objects close to the road are the most common subjects of tort claims against roadway agencies. The elements of hazard that need to be considered are the traffic exposure, the speed of traffic, the roadway alignment, the distance the roadside hazard is from the traveled way, and the size and severity of the roadside hazard. Larger, more rigid roadside objects that are closer to the edge of the traveled way on high-speed, high-traffic roadways command the most attention for improvement. Typical tort claims involve the following:

Faulty Guardrail Dimensions. Guardrail is intended as a safety device. Yet, many guardrails were installed before modern safety performance criteria were established in the late 1960's. As a result, many guardrails have 12.5-foot post spacing, where the standard since about 1966 has been 6.25-foot spacing. Many guardrails also have a 24-inch or lower beam height, where the standard since about 1966 has been 27 inches.

Faulty Guardrail End Treatments. Since about 1970, crashworthy end treatments have been available to eliminate the occurrence of colliding vehicles and their occupants being impaled on the guardrail. Yet, not only do many older guardrails remain in place without end treatments, but also many untreated ends have been installed since 1970, largely by uninformed or indifferent local roadway agencies.

Bridgerails and Culverts. Many roadways have old-style unprotected concrete parapet bridgerails or culverts, often at the edge of the traveled way. These bridgerails not only need guardrail protection for the bridgerail end and the steep slopes approaching the bridge, but they also need retrofitted rails to provide a smooth rail face across the bridge.

Utility Poles, Lightpoles, and Trees. These hazards are often placed very close to the edge of the traveled way, particularly in urban areas. When a pole or tree is placed within one foot of a curb face, an errant vehicle (because of its front overhang and angle of approach) can collide with the pole or tree even though the tires never leave the traveled way.

Steep Embankments. Foreslopes steeper than 4:1 are considered non-traversible. Foreslopes steeper than 3:1, on the average, will produce more severe occupant injuries than guardrail impacts. Despite the push for clear zones over the last 25 years, many sections of roadway still have unprotected 2:1 or steeper foreslopes close to the traveled way.


A long-recognized traffic safety principle is that drivers need sufficient visibility along the roadway to avoid collision. The criteria to apply this principle have been promulgated by the American Association of State Highway and Transportation Officials (AASHTO) and presented in a succession of design policies from 1931 to 1994. From a safety viewpoint, the most important of these are intersection sight distance, stopping sight distance, and rail-highway grade crossing sight distance. The first two of these are discussed here; rail-highway grade crossing sight triangles are discussed later.

When an uncontrolled highway or street intersection has serious sight obstructions, an extreme burden is placed on drivers to: (1) expect an intersecting vehicle; (2) judge what direction it might be coming from; (3) anticipate its speed; (4) judge their own closing rate to the conflict area; and (5) adjust their own speed and position to avoid collision once the conflicting vehicle is seen. This is a burden that few drivers handle well, particularly when the sight triangle is highly obstructed.

AASHTO2 calls for a minimum sight triangle for uncontrolled intersections where the sight line defines the hypotenuse of the triangle, and the legs of the triangle along each approach are a function of the operating speed of each roadway as shown in Table 1. Any sight distance more restricted than the Table 1 values should have stop or yield signs controlling one of the roadways.

For example, when two 50-mph roadways intersect, an open sight triangle, defined by two 400-foot legs measured along each roadway from the intersection, is needed to operate the uncontrolled intersection safely.

The U.S. has thousands of uncontrolled intersections. Typically, these intersections are found at the crossing of two low-volume local roads or streets. In rural areas, they are usually the intersections of two unpaved roads. In urban areas, they are usually the intersections of two local residential streets.

At urban uncontrolled intersections, sight obstructions are either houses, vegetation, or embankments close to the corner. At rural uncontrolled intersections, sight obstructions are usually vegetation (including seasonal crops) or embankments. Tort liability claims often involve sight triangles that are only 20-40% of those required by AASHTO.

When intersection sight distance is less than Table 1 values and cannot be improved, two-way stop signs are often the appropriate traffic control. Once stop signs are in place, a different set of criteria come into play for sight distance. A driver at a stop sign needs to see far enough down each intersecting approach to allow enough time to scan both approaches, make a decision to proceed, accelerate into the intersecting roadway, and then either cross, turn left, or turn right without collision. The AASHTO rule for crossing a major two-lane road, for example, is that the sight distance down the major road needs to equal 100 feet of sight distance for every 10 mph of speed on the major road. Again tort liability claims often involve sight triangles that are only 20-40% of those required by AASHTO.

Stopping sight distance (SSD) is another principle of safe roadway operations that recognizes that drivers need enough view of the road ahead to see and perceive an object in their path, to apply their brakes, and come to a stop before colliding with the object. The AASHTO stopping sight distance standards related to design speed are the same values as presented in Table 1.

Table 1
Isolated hillcrests with deficient SSD, may not have bad accident experiences unless other attendant roadway features are hidden by the crest to create traffic conflicts (intersections) or vehicle control problems (stop signs, sharp curves, Y intersections, etc.). When these kinds of attendant features are close to a hillcrest with less than 70% of the AASHTO stopping sight distance, accidents and tort claims can be expected unless special attention is devoted to installing compensating traffic control devices (warning signs, advisory speeds, extra delineation, etc.).

Unlike hillcrests, SSD restrictions on roadway curves are not produced by the roadway itself, but by roadside obstructions on the inside of the curve. Typical obstructions are vegetation, embankments, walls, fences, advertising signs, and buildings. A typical tort claim involves a head-on collision on a sharp curve with a narrow roadway where trees and other vegetation have grown close to the inside edge of the curve. Usually the vehicle taking the left-hand curve wanders over the centerline (a foreseeable event). The opposing driver, with very little sight distance and a relatively high closing rate, is surprised by the ensuing conflict and reacts by locking his brakes. Even if the wrong-side driver tries to evade the collision, the other vehicle often slides into his path.


In 1987, the Transportation Research Board8 determined that pavement edge drop hazards are greater than previously believed and pavement edge drops are a common source of tort claims against highway agencies. Considerable debate has occurred in courtrooms across the U.S., not only about what constitutes a hazardous edge drop, but also what duty roadway agencies have for either minimizing the occurrence of hazardous edge drops or warning of their existence.

Pavement edge drops can cause drivers to have unexpected collisions, particularly when they are surprised at night by the sudden drop of a wheel. Most commonly, the vehicle will be affected in one of three ways: (a) move abruptly across the travel lanes and either collide with opposing vehicles or roadside hazards off the far edge of the roadway; (b) overturn on the roadway or roadside; or (c) collide with roadside hazards beyond the edge drop.

The research has generally shown that the ability of a driver to recover from a pavement edge-drop excursion is a function of edge-drop height and shape, vehicle speed and path angle, and the width of lane available for recovery. Then too, certain vehicles such as motorcycles, sub-compact automobiles, and tractor-trailer trucks have a much greater sensitivity to edge drops than do the full-size automobiles that have normally been tested.

Many state roadway agencies have adopted a 3-inch edge height as a maximum level before maintenance should be done, based on the results of a study by Zimmer and Ivey8 (1982) and others. Other state roadway agencies have adopted a 1.5 - 2 inch criterion as a more appropriate maximum on 55-65 mph roadways, based on Olson and Zimmer10, Glennon11, or other studies that have both recommended these lower heights and also disputed the Zimmer and Ivey findings (which were based on the subjective ratings of a single pre-warned professional driver).

When pavement edge drops of 1.5 inches or more are a frequently recurring problem along a particular roadway, one or more of the following treatments should be used to either replace or supplement the normal maintenance practice of simply adding more shoulder material:
  1. Place low-shoulder warning signs.
  2. Add stabilizing material to the shoulder material, which is otherwise susceptible to rutting.
  3. Either pave the entire shoulder or pave at least a 2-3 foot strip of shoulder adjacent to the travel lane, particularly along the inside of roadway curves and where pavements are narrower than 22 feet.
The most effective way for roadway agencies to mitigate the present and future hazards associated with pavement/shoulder edge drops is to only issue pavement resurfacing contracts where providing a stabilized shoulder flush with the pavement surface is an integral part of the contract. In addition, all resurfacing contracts where the shoulder is unpaved should require a 45° or flatter bevel along the pavement edge.

The appropriate practice for pavement edge drops in construction work zones recognizes that the hazard with any edge drop progressively increases from a position off the shoulder, to the edge of the shoulder, to the edge of the traveled way, to between lanes, to within a travel lane, to in the wheel track of a lane. As this position hazard and the edge-drop height increase, the need for greater traffic control increases as does the expediency for minimizing the exposure to the edge drop through timely construction management. Pavement edge drops placed within a travel lane during resurfacing should generally be discouraged both because of the high exposure to contact and also because of the nearness of potentially conflicting traffic. Positive barriers should be placed where six-inch or higher edge drops are close to traffic, thus eliminating the high probability of vehicle rollover on contact with the edge.

Pavement edge drops at unpaved shoulders are a recurring nuisance particularly along narrower two-lane roadways with heavy truck traffic. Trucks not only blow away shoulder material during dry weather, but they also frequently disturb shoulder material by running with one wheel of a tandem overhanging the edge, particularly on the inside of highway curves. Then too, unstabilized shoulder material is highly susceptible to rutting by all vehicles during wet weather.


Principles and practices of traffic control for construction and maintenance work zones are well defined by the 1988 Manual on Uniform Traffic Control Devices1 (MUTCD), particularly if one refers to the 1993 revision of Part 6 dealing with these aspects. Tort liability cases involving construction and maintenance work zones most frequently claim a violation of the MUTCD.

The most commonly accepted principles for construction work zone safety are stated in Section 6A-5 of the MUTCD. These principles, which are frequently cited in construction zone cases, are:
  1. Assign traffic safety a high priority
  2. Apply the basic safety principles governing the design of permanent roadways.
  3. Prepare a traffic control plan.
  4. Avoid reduced speed zoning.
  5. Avoid frequent and abrupt changes in geometrics.
  6. Give drivers positive guidance approaching and throughout the work site.
  7. Remove traffic control devices that are inconsistent with intended travel paths.
  8. Inspect traffic control elements regularly to ensure intended operations.
  9. Assign individuals, who are trained in the principles of safe traffic control, the responsibility for safety at work sites.
  10. Maintain the roadside free of unnecessary hazards.
The most common (about 25% of total) tort claim in construction and maintenance work zones involves a pavement edge drop. Pavement edge drops occur on lane lines or at the edge of traveled way when resurfacing or excavating. Edge drops of 1.5 inches or greater within the traveled way are clearly a hazard to avoid. Lower edge drops should be warned of with signs and eliminated as quickly as possible. Edge drops of 2 inches or more within or at the edge of the traveled way should be shielded with channelizing devices and warning signs. Because edge drops of 6 inches or more are likely to cause vehicle undercarriage contact and subsequent rollover, positive barriers should be considered for these conditions.

Faulty transition areas are cited in about 20% of construction and maintenance zone claims. The specifics of these claims often include: (a) the taper was too short for a lane closure; (b) the median crossover had too low of a design speed; (c) the zone lacked adequate warning signs and channelizing devices; and (4) the lane closure was too close to a crossover.

Another 20% of construction and maintenance zone claims involve a road-closure problem. Most typically, advance warning signs are missing or ill-placed. Non-standard warning signs are sometimes used. Then too, the required Type III barricade is sometimes missing at the point of closure.

The other major category (about 15%) of claims for construction or maintenance work zones involves slow-moving maintenance vehicles. These vehicles present a special hazard to motorists on high-speed roadways because they violate driver expectancies, particularly when the sight distance is marginal or poor. Unfortunately, maintenance workers are often inadequately trained and may be oblivious to the hazards they create. The most common claim in this category is the lack of adequate advance warning.


Safety at rail-highway grade crossings has long been a subject of public concern. No other classification of motor-vehicle accident has such a high severity, making this a safety issue of primary significance.

Of the 168,000 public rail-highway grade crossings in the United States, about 68,000 are protected by active warning systems. Of the remaining 100,000 crossings, about 9,000 have no protective devices and about 91,000 have some form of passive protection (static signs and markings). These passive devices only inform the driver of the existence and location of the crossing. For brevity, this discussion will be limited to passive crossings, which are the subject of the majority of tort liability claims.

In 1973, the U.S. Congress passed the Federal Highway Safety Act that first allocated funding for safety improvements at rail-highway grade crossings. Current annual federal expenditures are in the $250 million range, with most of these funds spent on major improvements such as grade separations, highway realignment, and flashing signals and gates. In comparison, very little money is spent to upgrade the tens of thousands of lower-volume, passive crossings.

The vehicle-train conflict is similar to the vehicle-pedestrian conflict at pedestrian crosswalks and the right-angle vehicle-vehicle conflict at street intersections. Quite often, sight distance is restricted. Sometimes distracting elements are present. Then too, driver perception of an ensuing conflict is difficult at night. But the most critical factors are the vehicle speeds and separation distances at the time the driver perceives a potential collision. If, at the time of conflict perception, the speeds are too great and the distances too small, a collision is inevitable.

When drivers approach a crossing, they first need to know that the crossing is there and, second, if a train is on the crossing, approaching the crossing, or not in the vicinity of the crossing. They also may need guidance on how to safely approach and traverse the crossing. At passively-controlled crossings, the driver's task of traversing the crossing can be made more hazardous by any of the following defects:

Sight-Restricted Crossing. A driver approaching a grade crossing will reach the vertex of a critical sight triangle where a decision must be made to stop if an approaching train is also within the triangle. The required sight triangle is a function of both the roadway speed and track speed. When existing sight restrictions at a crossing allow the driver to pass that critical point without seeing a nearby train, the driver has difficulty either braking or proceeding through the crossing without colliding with the train.

Sight triangle dimensions are given in the Railroad Highway Grade Crossing Handbook4, the Traffic Control Devices Handbook5, and in the AASHTO, A Policy on Geometric Design of Highways and Streets2. The AASHTO Policy has slightly higher values than the other two sources. The values from the other two sources are shown in Table 2.

Whenever a deficient sight triangle is allowed to exist at a grade crossing, all of the burden is put on the driver to know that the sight restriction is hazardous and to determine what speed is appropriate for the crossing. This is a task that many drivers do not handle well.

Clearing sight obstructions, such as brush and weeds, from a grade crossing not only provides adequate sight distance at a crossing, but can also provide a better preview of the crossing for approaching drivers. When adequate sight triangles cannot be maintained at a passive grade crossing, stop signs (or ultimately flashing signals) can be an effective countermeasure. Once stop signs are installed, a different sight distance criterion applies. A driver at a stop sign needs to see far enough down each leg of the track to allow enough time to scan both directions, make a decision to proceed, accelerate, and clear the crossing (see column for 0 mph Assumed Vehicle Speed in Table 2).

Roadway Intersections Close to the Crossing. Over 35% of public rail-highway crossings have a roadway intersection within 75 feet of the tracks. Usually this occurs when a major roadway is close to and runs parallels to the track, and a minor roadway intersects both the major roadway and the track. These crossings generally have a higher occurrence of accidents because of several inherent deficiencies.

The major difficulty for these crossings lies with the driver who is turning off of the major roadway toward the crossing. This driver will not have a preview of a train that is approaching from behind until the vehicle turns onto the minor roadway and is squared up toward the crossing. In effect, the available sight distance triangle may often only be safe for roadway speeds of 5 mph or less.

This kind of crossing also presents particular problems for long vehicles on the minor roadway that have to stop on the tracks before entering the major roadway. These vehicle have additional difficulty turning from the major roadway when a train is coming because they may end up blocking major road traffic when they stop for the train.

Sharp Crossing Intersection Angle. Sharp crossing angles present a similar problem as sight-restricted crossings and crossings with nearby intersections. Drivers, particular in large trucks, approaching a crossing either cannot or will not look back over their shoulder to search for a train.

Poor Visibility of the Train at Night. Train cars are often dirty and painted dark colors, giving them little contrast with the background. As a result, approaching drivers cannot see a train that is already on a dark crossing as they approach at night.

Backing up the existing far-side crossbuck with another retroreflective crossbuck is an inexpensive countermeasure to accidents where vehicle run into the side of trains at night. At night, on a dark crossing, when a moving train is already on the crossing as a vehicle approaches, a properly positioned far-side crossbuck will reflect the vehicle's headlights back to the driver through the gaps between the cars. This alternating on-off effect caused by the gaps between the moving cars approximates an active warning device and serves to alert the driver to the presence of a moving train on the tracks.

Rough Crossings. When a crossing surface is rough or uneven, a driver's attention may be devoted primarily to choosing the smoothest path over the crossing, rather than scanning both track directions for an approaching train. This undesirable behavior will be particularly conditioned if the driver is consistently exposed to rough or uneven crossings.

Steep Crossing Approaches. Steep crossing approaches have several attendant hazards. They distract drivers from searching for trains because of the extra attention needed to both negotiate the grade and to scan for conflicting opposing vehicles hidden by the crest. They cause particular dangers for drivers under icy winter conditions; and, they can cause longer trucks to high-center on the crossing. For these reasons, many states prohibit crossing grades steeper than about six percent. Many existing crossings, however, often violate these state laws on maximum grade.



A majority of tort claims for serious injuries or death involve roadway design or traffic control elements that are significantly deficient when compared to acceptable roadway safety practices and principles. Common defects are non-forgiving roadsides, faulty guardrails, sight obstructions, dangerous pavement edge drops, faulty work zone layouts, and sight-obstructed rail-highway grade crossings. These major defects occur more frequently on local (county, township, city) roads where the training and understanding of the consequences of deficient roadway elements is not adequate.


1. U.S. Department of Transportation, Federal Highway Administration, Manual on Uniform Traffic Control Devices, Washington, D.C., 2001.

2. American Association of State Highway and Transportation Officials, A Policy on Geometric Design of Highways and Streets, Washington, D.C., 2001.

3. American Association of State Highway and Transportation Officials, Roadside Design Guide, Washington, D.C., 1988.

4. Tustin, B., Richards, H., McGee, H. & Patterson, R., Railroad-Highway Grade Crossing Handbook, U.S. Department of Transportation, Federal Highway Administration, Washington, D.C., 1986.

5. Department of Transportation, Federal Highway Administration, Traffic Control Devices Handbook, Washington, D.C., 1983.

6. American Association of State Highway and Transportation Officials, AASHTO Maintenance Manual, Washington, D.C., 1987.

7. Pline, J., Traffic Engineering Handbook, Institute of Transportation Engineers, Washington, D.C., 1999.

8. Transportation Research Board, Designing Safer Roads, Special Report 214, 1987.

9. Zimmer, R. & Ivey, D., Pavement Edges and Vehicle Stability -- A Basis for Maintenance Guidelines, Texas Transportation Institute, College Station, Texas, 1982.

10. Olson, P., Zimmer, R. & Pezoldt, V., Pavement Edge Drop, Transportation Research Board, Washington, D.C., 1986.

11. Glennon, J., "Effects of Pavement/Shoulder Drop-Offs on Highway Safety", State of the Art Report 6, Transportation Research Board, Washington, D.C., 1987.

About the Author

Dr. John C. Glennon is a traffic engineer with over 45 years experience. He has over 120 publications. He is the author of the book "Roadway Safety and Tort Liability" and is frequently called to testify both about roadway defects and as a crash reconstructionist.


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