The Safety of Roadway Features
John C. Glennon, D. Engr., P.E.
April 2005 (copyright)
John C. Glennon, D. Engr., P.E.
April 2005 (copyright)
Despite exceptional progress in reducing U.S. roadway collision rates and fatalities over the last 30 years, roadway defects are still common. Even with many advances in roadway safety technology, several kinds of roadway defects still persist. Many roadway conditions particularly on our older roadways have become exceedingly more hazardous as we have systematically increased speed limits.
Typical hazards that seem all too common are dangerous hydroplaning sections, severe pavement edge drop offs, and ill-conceived or improperly signed construction work zones. Then too, there remains thousands of sight-restricted intersections and railroad grade crossings, spear-end guardrails, non-crashworthy bridgerails, and hidden, unmarked or ill-marked roadway curves and intersections.
This paper categorizes these common roadway defects, highlights the related roadway design, traffic control, and roadway maintenance applications, and lists authoritative and other key references.
A. Roadside Features
- The Challenge
A major portion of all collisions involve a single vehicle running off the road, particularly on rural high-speed roadways.
- Basic Application
To design and/or maintain a forgiving roadside - a roadside that either has a clear recovery zone or where such a zone is not possible has a roadside barrier in place.
- Rules of Thumb
a. Remove, redesign, or protect roadside hazards within 30 feet of the traveled way on freeways (interstates) or within 20 feet on other roadways.
b. Hazards protected by traffic barriers should have more severe impact consequences than the traffic barrier.
- Typical Hazardous Conditions
a. Steep side slopes in the clear zone.
b. Bridge structures in the clear zone.
c. Trees in the clear zone.
d. Utility poles in the clear zone.
e. Drainage structures in the clear zone.
f. Non-crashworthy or ill-placed traffic barriers and bridgerails.
- Authoritative References
American Association of State Highway and Transportation Officials, Roadside Design Guide, 1989, 1996, and 2001.
American Association of State Highway and Transportation Officials, Guide for Selecting Locating and Designing Traffic Barriers, 1977.
- Other Key References
Federal Highway Administration, A Handbook of Highway Safety Design and Operating Practices, 1968, 1973, and 1978.
John C. Glennon and Paul F. Hill, Roadway Safety and Tort Liability, Lawyers and Judges Publishing Co., 2004.
B. Hydroplaning Sections
- The Challenge
Where roadway slopes, structures, and/or pavement conditions allow water to pond or to build up and flow across the pavement.
- Basic Application
Design and/or maintain the roadway to have adequate slopes and pavement texture, drainage facilities to reasonably drain heavier rainfalls, and a surface free of wheel ruts.
- Rule of Thumb
Hydroplaning can be expected for speeds above 45 mph where water flows or ponds to depths of 1/10 inch or more over a length of 30 feet or more.
- Typical Hazardous Conditions (usually two or more conditions combine to create the hazard).
a. Inadequate cross slopes.
b. Rutted wheel tracks.
c. Polished pavement.
d. Curve transition area.
e. Steep downgrades.
f. Water drained to pavement from culverts, ditches, and side roads.
g. Build up of turf shoulder, which dams water against pavement edge.
h. Sag vertical curves.
- Authoritative References
American Association of State Highway And Transportation Officials, A Policy on Geometric Design of Highways and Streets, 1984, 1990, 1994, 2001, 2004 and similar preceding policies.
- Other Key References
B. M. Gallaway and Jerry G. Rose, The Effects of Rainfall Intensity, Pavement Cross Slope, Surface Texture, and Drainage Length on Pavement Water Depths, Texas Transportation Institute, Research Report No. 138-5, 1971.
G. G. Balmer and B. M. Gallaway, Pavement Design and Controls for Minimizing Automotive Hydroplaning and Increasing Traction, American Society of Testing and Materials, ASTM STP 793, 1983.
B. M. Gallaway, et. al., Pavement and Geometric Design Criteria for Minimizing Hydroplaning, Federal Highway Administration, Report No. FHWA-RD-79-31, 1979.
R. Scott Heubner, David A. Anderson, and John C. Warner, Proposed Design Guidelines for Reducing Hydroplaning on New and Rehabilitated Pavements. National Cooperative Highway Research Program, Research Results Digest Number 243, September 1999.
R. S. Heubner, PAVDRN Computer Program with User's Guide, NCHRP Project 1-29, Improved Surface Drainage of Pavements, Transportation Research Board, June 1998.
John C. Glennon and Paul F. Hill, Roadway Safety and Tort Liability, Lawyers and Judges Publishing Co., 2004.
C. Pavement Edge Drop Offs
- The Challenge
Pavement edge drop offs can create loss of control for motorists, who inadvertently drive off the edge of the traveled way at highway speeds.
- Basic Application
Based on the body of research literature, the majority of State DOT's regard pavement edge drop offs of 1½ - 2 inches as needing remedial treatment.
- Rules of Thumb
a. Vertical or near-vertical edge drops of two inches or more can cause slingshot accidents even at lower speeds.
b. Edge drops of six inches or more will cause vehicle undercarriage contact, often resulting in rollover.
- Typical Hazardous Conditions
a. Edge drop offs of two inches or greater for 55-mph or greater roadways.
b. Vertical edges are more hazardous.
c. Narrow roadways create more opportunity for an edge-drop encounter.
d. Drop-offs within the traveled way in construction work zones.
e. Repaved roadways where the unpaved shoulder was not treated leaving a hazardous drop off.
f. Unpaved shoulders that, because of the lack of maintenance, become eroded or rutted.
- Authoritative References
American Association of State Highway Officials, A Policy on Geometric Design of Rural Highways, 1954.
American Association of State Highway Officials, A Policy on Geometric Design of Rural Highways, 1965.
Federal Highway Administration, Handbook of Highway Safety Design and Operating Practices, 1968, 1973, and 1978 eds.
Federal Highway Administration, Traffic Control Devices Handbook, 1983, 2001.
American Association of State Highway and Transportation Officials, Roadside Design Guide, 1989, 1996, 2001.
Federal Highway Administration, Maintenance and Highway Safety Handbook, 1977.
- Other Key References
P. L. Olson, R. A. Zimmer, and V. Pezoldt, Pavement Edge Drop, Transportation Research Board, 1986. Available from www.criterionpress.com.
J. L. Graham and John C. Glennon, Work Zone Design Considerations for Truck Operations and Pavement/Shoulder Drop-Offs, Federal Highway Administration, 1984.
John C. Glennon, Effect of Pavement/Shoulder Drop-Offs on Highway Safety: A Synthesis of Prior Research, Transportation Research Board, 1985, Available from www.criterionpress.com.
D. L. Ivey, et al., Safety in Construction Zones Where Pavement Edges and Drop Offs Exist, Transportation Research Record 1163, 1988.
Criterion Press, Excerpts of Key Documents Related to Pavement Edge Drop-Offs, 2000. Available from www.criterionpress.com.
John C. Glennon and Paul F. Hill, Roadway Safety and Tort Liability, Lawyer and Judges Publishing Co., 2004. Available from www.criterionpress.com.
J. B. Humphreys and J. A. Parham, The Elimination or Mitigation of Hazards Associated with Pavement Edge Drop-Offs During Roadway Resurfacing, AAA Foundation for Traffic Safety, 1994.
- Interesting WEB SITES
D. Sight Distance Obstructions
- The Challenge
Hillcrests, vegetation, and/or structures occasionally restrict a driver's sight and thereby hamper safe travel ahead or through intersections.
- Basic Applications
Standards for stopping sight distance and intersection sight distance allow drivers adequate time to see conflicting objects or vehicles, respond, and avoid collision as a function of expected speed.
- Rules of Thumb
a. Sight obstructions often restrict sight distances to considerably less than standard values.
b. Sight obstructions ahead are most detrimental when they hide intersections, sharp roadway curves, narrow bridges, etc.
c. Needed intersection sight distances for high-speed roadways are in the hundreds of feet.
- Typical Hazardous Conditions
a. Hidden intersections.
b. Hidden signs.
c. Hidden roadway curves.
d. Hidden conflicting vehicles.
- Authoritative References
American Association of State Highway and Transportation Officials, A Policy on Geometric Design of Roadways and Streets, 1984, 1990, 1994, 2001, 2004 and similar preceding policies.
- Other Key References
John C. Glennon, Effect of Sight Distance on Highway Safety, in Relationship Between Safety and Key Highway Features: A Synthesis of Prior Research, Transportation Research Board, 1987.
T. R. Neuman, John C. Glennon, and J. E. Leisch, Functional Analysis of Stopping Sight Distance Requirements, Transportation Research Record 923, Transportation Research Board, 1984.
John C. Glennon, Geometric Design: Sight Distance, in The Traffic Safety Toolbox, Institute of Transportation Engineers, 1993.
John C. Glennon and Paul F. Hill, Roadway Safety and Tort Liability, Lawyers and Judges Publishing Co., 2004.
E. Roadway Curves
- The Challenge
Older roadways with sharp roadway curves often have other sub-standard geometrics and/or missing or deficient warnings.
- Basic Application
To design roadway curves to accommodate expected speeds. For existing curves with safe speeds less than expected speeds, appropriate traffic control devices need to be placed, including: advance warning signs, delineators, large arrow signs, and/or chevrons.
- Rules of Thumb
a. Roadway curves are particularly dangerous when they have a safe speed that is 15 mph or more below the speed limit.
b. Roadway curves with safe speeds of 25 mph or less are very dangerous on highways with speed limits of 55 mph or more. Extraordinary traffic control techniques are necessary for any measure of safety.
- Typical Hazardous Conditions
a. Sharp curves, particularly with safe speed below 30 mph on high-speed roadways.
b. Sharp curves with no signing or delineation.
c. Sharp curves hidden over sharp hillcrests with inadequate warning signs.
d. Inadequate of reverse superelevation (banking).
e. Sight obstructions across the inside of curves.
f. Tangent intersection, which may give false visual cues about the proper path.
g. Rough or uneven pavement.
h. Low skid resistance.
i. Hazardous roadside.
j. Loose material on pavement.
k. Sharp reverse curves too close together.
l. Narrow roadway.
- Authoritative References
American Association of State Highway and Transportation Officials, A Policy on Geometric Design of Streets and Highways, 1984, 1996, 1994, 2001, 2004, and similar preceding documents.
Federal Highway Administration, Manual on Uniform Traffic Control Devices, 1988, 2001, 2004.
Kansas Department of Transportation, Handbook of Traffic Control Practices for Low Volume Rural Roads, 1991.
Federal Highway Administration, Traffic Control Devices Handbook, 1983.
- Other Key References
John C. Glennon, T. R. Neuman, and J. E. Leisch, Safety and Operational Considerations for Design of Rural Highway Curves, Federal Highway Administration, 1983.
John C. Glennon, Effect of Alinement on Highway Safety, Transportation Research Board, State of the Art Report 6, 1987.
John C. Glennon, and Graeme D. Weaver, Highway Curve Design for Safe Vehicle Operations, Highway Research Record 371, 1972.
John C. Glennon and Paul F. Hill, Roadway Safety and Tort Liability, Lawyers and Judges Publishing Co., 2004.
F. Railroad Grade Crossings
- The Challenge
Trains running on tracks need very long distances to brake. Therefore, when there's a conflict with a roadway vehicle, the train is essentially running out of control.
- Basic Application
To maintain a crossing free of sight obstructions with adequate traffic controls for the speed and volume of traffic.
- Rules of Thumb
a. Adequate sight triangles are key to safety at crossbuck-only crossings.
b. Large trucks are at risk, even with marginally acceptable sight triangles.
c. Drivers have difficulty seeing dark trains at crossbuck-only crossings at night.
d. Sharp roadway approach angles and close intersections severely hamper effective sight triangles.
- Typical Hazardous Conditions
a. Severely restricted sight triangles.
b. Intersections close to the crossing.
c. Sharp-angled crossing approaches.
d. Poor maintenance of signs.
e. Lack of advance warnings.
f. Poor visibility of flashing signals.
g. Malfunctioning of flashing signals and/or gates.
h. Steep crossing grades.
i. Rough crossing surfaces.
- Authoritative References
B. H. Tustin, et. al., Railroad-Highway Grade Crossing Handbook, Federal Highway Administration, September, 1986.
Federal Highway Administration, Manual on Uniform Traffic Control Devices, 1988, 2001, 2004.
Federal Highway Administration, Traffic Control Devices Handbook, 1983, 2001.
American Association of State Highway and Transportation Officials, A Policy on Geometric Design of Highways and Streets, 1990, 1994, 2001, 2004.
National Committee on Uniform Traffic Laws and Ordinances, Uniform Vehicle Code and Model Traffic Ordinances, 1992.
American Railway Engineering Association, Manual for Railway Engineering, 1981.
- Other Key References
Federal Railroad Administration, Rail-Highway Crossing Accident/Incident and Inventory Bulletin, calendar-year publications.
National Transportation Safety Board, Passenger/Commuter Train and Motor Vehicle Collisions at Grade Crossings, 1985.
Kay Fitzpatrick, John M. Mason, Jr., and John C. Glennon, Sight Distance Requirements for Trucks at Railroad-Highway Grade Crossings, Transportation Research Record 1208, 1989.
Karl Knoblauch, Wayne Hucke, and William Berg, Rail Highway Crossing Accident Causation Study, Federal Highway Administration, 1982.
John C. Glennon and Paul F. Hill, Roadway Safety and Tort Liability, Lawyers and Judges Publishing Co., 2004.
G. Construction and Maintenance Work Zones
- The Challenge
The Safety responsibility for work zones often rests with contract workers and/or highway agency construction engineers, neither of who are usually adequately trained to grasp basic roadway safety principles that are extraordinarily important in work zone.
- Basic Application
To design and layout work zones with temporary traffic control devices that provide drivers with clear and positive guidance approaching and traveling through the zone.
- Rule of Thumb
If something seems wrong with the temporary traffic control in a work zone, there is probably one or more violations for the Manual on Uniform Traffic Control Devices.
- Hazardous Conditions
a. Lane drop taper is too short.
b. Median crossover is designed with low safe speed curvature.
c. Lack of adequate advance warning signs.
d. Pavement edge drop offs that are close to or within the traveled way.
e. Road closures that are improperly signed.
f. Slow-moving maintenance vehicle without adequate rearward warnings.
g. Lane closures that back traffic past all work zone warning signs.
- Authoritative References
Federal Highway Administration, Manual on Uniform Traffic Control Devices, 1988, 2001, 2004.
Federal Highway Administration, Part 6, Standards and Guides for Traffic Controls for Street and Highway Construction, Maintenance, Utility, and Incident Management Operations, Revision 3 of the 1988 Edition of the Manual on Uniform Traffic Control Devices, September 3, 1993.
Federal Highway Administration, Federal Aid Highway Program Manual, Volume 6, Chapter 4 Section 2, Subsection 12, October 13, 1978, amended July 1, 1982.
d. Federal Highway Administration,Traffic Control Devices Handbook, 1983, 2001.
- Other Key References
Jerry L. Graham, Robert J. Paulsen, and John C. Glennon, Accident and Speed Studies in Construction Zones, Federal Highway Administration, 1977.
E. C. Noel, et. al., Work Zone Traffic Management Synthesis, 5 volumes, Federal Highway Administration, 1989.
John C. Glennon and Paul F. Hill, Roadway Safety and Tort Liability, Lawyers and Judges Publishing Co., 2004.
H. Traffic Control Devices
- The Challenge
Needed traffic control devices are often not installed or are installed in a faulty manner by persons who are inadequately trained about the basics of traffic safety.
- Basic Application Traffic control devices should be installed by qualified traffic engineers with a keen knowledge of basic safety principles and the application of the Manual on Uniform Traffic Control Devices.
- Rule of Thumb Although properly designed and installed traffic controls should benefit all drivers, they should be designed for the unfamiliar driver.
- Typical Hazards
a. Stop signs and/or traffic signals hidden over a sharp hillcrest or around a sharp curve.
b. Non-reflective signs.
c. Poorly aimed traffic signals.
d. Failure to place warning devices.
e. Unclear messages.
f. Non-standard signs.
g. Damage signs.
h. Missing End of Road markers.
i. Ill-marked obstruction within the roadway.
j. Missing or faded pavement markings.
k. Isolated traffic signals on a high-speed roadway.
l. Traffic signals with yellow clearance phases that are too short.
- Authoritative References
Federal Highway Administration, Manual on Uniform Traffic Control Devices, 1988, 2001, 2004.
Federal Roadway Administration, Traffic Control Devices Handbook, 1983, 2001.
Institute of Transportation Engineers, Traffic Engineering Handbook, Fifth Edition, 2001.
- Other Key References
G. J. Alexander and H. Lunenfeld, Positive Guidance in Traffic Control, Federal Highway Administration, 1975.
G. J. Alexander and H. Lunenfeld, Driver Expectancy in Highway Design and Engineering, Federal Highway Administration, 1986.
John C. Glennon and Paul F. Hill, Roadway Safety and Tort Liability, Lawyers and Judges Publishing Co., 2004.
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.
RESUME OF JOHN C. GLENNON
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.
RESUME OF JOHN C. GLENNON
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