The NCDOT spends hundreds of millions of dollars each year widening old two-lane roads with 55 mph speed limits into multilane highways. Sometimes on those multilane highways the Department has to construct vertical curbs for access control or other reasons. Since there is clear and well-known guidance that vertical curbs should not be placed next to high-speed lanes, the NCDOT typically uses a lower design speed (50 mph) and posted speed limit (usually 45 mph) on such segments. This lower speed limit creates an enforcement problem, as drivers do not perceive danger from the curbs and try to travel at least as fast as they did before the road was improved.The NCDOT needs better information to avoid the scenario described above. Specifically, the NCDOT needs answers to two key questions:Do vertical curbs next to high-speed lanes really cause more frequent and severe collisions than other cross-section choices? The crash test research is clear, but evidence from collision data is much less convincing.If vertical curbs are more dangerous, is a lower speed limit the best way to alert the public to this danger or are there other treatments that the NCDOT should use?
The purpose of this research is to answer those questions for North Carolina roadways. With answers to those questions, the NCDOT can avoid the scenario described above.The main effort in this research will be to find a sample of higher-speed roads with vertical curbs with 45 mph and 55 mph speed limits and examine the collision records and vehicle speed distributions on those roads. The primary research product will be a summary report documenting the answers to the questions and any recommendations based on those answers. The summary report will serve the NCDOT as a technical reference when designing roads with vertical curbs and establishing speed limits on such roads. The report should also be circulated to the State Highway Patrol and other police agencies that enforce those speed limits."
