United States Department of Transportation
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Edition:Interim: September 1993 - August 1994
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Abstract:Providing effective roadside warning devices for drivers of large trucks is critical on freeway connectors where speeds are relatively high, but design speeds may be substantially lower than on main lanes. Identifying and testing appropriate methods of monitoring traffic on freeway connectors was included in an earlier phase of this research. Two monitoring systems evolved, one using roadway sensors and the other using roadside sensors. Roadway sensors consisted of both piezoelectric and inductive loop sensors, while roadside sensors applied infrared sensor technology. The roadway warning devices tested can be categorized as passive devices and active devices. Passive devices consisted of "truck tipping" warning signs, while the active device consisted of flashing lights mounted one above and one below a set of passive truck tipping signs on both sides of the roadway. Speed reduction, as associated with accident reduction, was the ultimate goal of these tests. The null hypothesis tested by ANOV A of no treatment effect in the presence of initial speed was rejected in all but one of four models, using the probability of a Type I error, a, equal 0.05. Speed reductions due to the active system were significant downstream of the first curve on the connector, suggesting that truck drivers reduced speeds due to the lights, but beyond the desired location. Cumulative speed distributions showed that the fastest trucks decreased their speeds by approximately 3 to 5 km/h (2 to 3 mi/h) during the test period. Five of the seven single-vehicle truck accidents recorded on the 1-61O/US-59 connector in an 8 1/2-year period were speed-related, resulting in rollover. None occurred after installation of warning treatments being tested, although there were other prior years before treatment with no recorded accidents.
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