U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000
Comparison of nominal and substantive concepts of safety | |
NCHRP Report 500 series | |
Steps in the design exception process | |
Advanced technology is making the collection of in-service data more effective and more efficient | |
Because it is a design control, design speed affects the curvature, stopping sight distance, superelevation, and other features of this horizontal curve | |
Accident Modification Factors for lane width on rural two-lane highways | |
Shoulders on this urban freeway provide enough width for crash avoidance, storage of disabled vehicles, maintenance activities, and enforcement | |
Partially-paved shoulders on this rural arterial improve bicycle accommodation and reduce risky passing maneuvers | |
Pavement edge drop-off | |
Comparison of how shoulder width affects stopping sight distance past concrete bridge rail along horizontal curves | |
Accident Modification Factors for shoulder width on rural two-lane highways | |
Bridge width | |
Vehicle shying towards the centerline on a narrow bridge | |
Horizontal alignment | |
Superelevation | |
Horizontal curve at the base of a steep grade | |
Vertical stopping sight distance at a crest vertical curve | |
Headlight sight distance at a sag vertical curve | |
Sight distance at an undercrossing | |
Horizontal stopping sight distance | |
Not all locations with limited stopping sight distance are the same in terms of safety risk | |
Stopping sight distance profile | |
Cross-slope break on the high side of a superelevated curve | |
Interstate closure after an impact with a bridge | |
Lateral offset to obstruction is an operational offset and is not the same as clear zone | |
Signs can be used to warn drivers in advance of a change in lane width | |
Wide pavement markings | |
Recessed pavement markings | |
Raised pavement markings | |
Post-mounted delineators | |
Lighting | |
Shoulder rumble strips | |
Centerline rumble strips | |
Painted edgeline rumble strips | |
Partially paved shoulders | |
Safety edge (top) and after the shoulder has been graded over the edge (bottom) | |
Fixed object removal. Separate box culverts were extended, connected, and covered at this interchange | |
Breakaway light poles | |
Shielding fixed objects with barrier | |
Pull-off area on the inside of a horizontal curve | |
Signs can be used to warn drivers in advance of a narrow bridge | |
Reflector tabs on guardrail | |
Object markers and post-mounted delineators at a narrow bridge | |
White concrete bridge rail | |
Anti-icing system on a bridge | |
Bridge rail and guardrail transition in compliance with NCHRP Report 350 | |
Turn warning sign with flashing beacon | |
Curve warning sign. | |
Dynamic curve warning system | |
Delineation with large chevrons | |
Delineation with post-mounted delineators | |
Delineations with reflectors on barrier | |
Advance warning of a steep grade | |
Climbing lane | |
Truck escape ramp | |
Continuous drainage system | |
Sign for crest vertical curve with inadequate stopping sight distance | |
Intersection warning sign with flashers activated by vehicles entering from the side road | |
A STOP sign with a flashing beacon improves visibility of the sign at this intersection with limited vertical sight distance | |
Intersection lighting | |
SLIPPERY WHEN WET sign | |
Longitudinal texture applied to fresh pavement to improve surface friction | |
Transverse grooving to improve surface drainage and friction | |
An example of transitioning the cross slope of the shoulder to mitigate a cross-slope break greater than 8% | |
Vertical clearance signing | |
Vertical clearance signing | |
Warning sign with hanging chimes installed at the same height as the vertical clearance of the structure | |
Reflective sheeting on utility poles | |
Reflective sheeting on utility poles | |
The project runs through Des Moines, Iowa | |
Approximate project limits of design exception | |
Interstate 235 before reconstruction | |
Interstate 235 after reconstruction | |
Cross section within the unconstrained locations | |
The unconstrained cross section | |
Cross section within the area of restricted width | |
Narrower lane widths would place the lane lines in a different transverse position than the underlying longitudinal joints | |
Inside lane and shoulder widths within the constrained areas were narrowed | |
Lighting was placed on the outside of the freeway through the design exception area | |
Lighting was placed down the center of the median where more cross-sectional width was available | |
The project is located in north-central Wyoming | |
Approximate project limits | |
The steep cut on the north side of the highway and deep canyon on the south illustrate the difficult terrain faced by designers | |
The Tensleep-Buffalo Highway leads into the Big Horn National Forest in the Rocky Mountains | |
A massive retaining wall illustrates the difficult site constraints that were encountered | |
Signing for the steep grades is provided throughout the project | |
Electronic signing provides enhanced warning for the non-standard horizontal curves | |
Advance signing for the truck escape ramp | |
Advance signing for the brake-check turnout | |
A pull-off area provides tourist information and spectacular views | |
Runaway truck ramp with arrestor system | |
Runaway truck ramp | |
Electronic signing provides advance warning when the truck ramp is closed | |
Climbing lane | |
Guardrail on the outside of a horizontal curve | |
State Route 99 is an urban arterial in Seattle, Washington | |
State Route 99 parallels Interstate 5 through the Seattle metro area | |
SR 99 before and after reconstruction in Des Moines | |
SR 99 before and after reconstruction in SeaTac (top) and Shoreline (bottom) | |
Drawing of proposed improvements to SR 99 in Shoreline | |
Left-turn lane and U-turn areas after reconstruction in Federal Way | |
New transit stop in Des Moines | |
SR 99 before and after reconstruction in Des Moines | |
Median tree plantings along SR 99 in SeaTac | |
Impact with tree in median (SeaTac) | |
Information from City maintenance personnel provided data on tree impacts that were not reported | |
When the in-service evaluation showed that many tree hits were occurring
at the narrow-median locations adjacent to turn lanes, trees were no longer | |
A low-profile barrier was used along the median of SR 99 in Des Moines. | |
Sloped-down end section adjacent to turn lane | |
Two low-profile barriers have passed NCHRP Report 350 test-level 2 (45 mph) crash testing | |
Los Angeles, California | |
State Route 110. The Arroyo Seco Parkway | |
SR 110 shortly after construction in 1940 | |
Historic structures along the Arroyo Seco Parkway | |
The San Gabriel Mountains on the horizon illustrate the Parkways scenic context | |
The Arroyo Seco Parkway has a narrow cross section, a curvilinear alignment, and non-standard interchange geometry | |
The Arroyo Seco Channel runs adjacent to the Parkway, constraining its width on one side | |
Single-slope concrete median barrier at a horizontal curve | |
Pull-off areas provided periodically along the outside lanes | |
Enhanced delineation with raised pavement markers and pavement markings with high retroreflectivity | |
Warning signs for curvature, slowing traffic, and vertical clearance | |
Geometry at the State Street Exit Ramp |