Quantifying safety and speed data for rural roundabouts with high-speed approaches

If transportation agencies are going to move Towards Zero Deaths on their roadways, it will be essential to address the thousands of fatal and injury crashes occurring at intersections. With nearly 3,000 fatalities at rural intersections annually, better intersection designs are critical. Roundabouts are a proven safety countermeasure, but until this point the safety data for rural roundabouts on high speed roadways has been limited. This research conducted an in depth safety and approach speed data analysis for rural roundabouts on high speed roadways and provides the first published planning level crash prediction model available for rural roundabouts. Crash analysis results showed that rural roundabouts with high speed approaches significantly reduced total crashes by 62 to 68 % and injury crashes by 85 to 88 % at nineteen rural roundabouts. Moreover, the number of angle crashes, which tend to have a higher likelihood of causing injuries at high speeds, were reduced by 83%, also a statistically significant reduction. Approach speed data proved that drivers are able to slow down in advance of roundabouts on rural roadways and the mean speeds at 100 ft from the yield line were 2.5 mph lower than mean speeds at 100 ft from the stop bar at stop controlled approaches. Additionally, a comparison between roundabout approaches with and without rumble strips showed mean speeds 4.3 mph and 3.3 mph lower at 100 ft and 250 ft from the yield line, respectively, for the approaches with rumble strips; however, the variation in speeds increased with the introduction of rumble strips. The results of this research support decision-making to invest in an intersection alternative that lowers speeds and significantly reduces the risk of injury crashes. Roundabouts eradicate the risk of drivers running stop signs and red lights. Roundabouts save lives

EVALUATING SPEED DIFFERENCES BETWEEN PASSENGER VEHICLES AND HEAVY TRUCKS FOR TRANSPORTATION-RELATED EMISSION MODELING

Heavy vehicles emit emissions at different rates than passenger vehicles. They may behave differently on the road as well, yet they are often treated similarly to passenger vehicles in emissions modeling. Although not frequently considered in calculating emission rates, differences in the operating speeds of passenger vehicles and heavy trucks may influence emissions. The main goal of this research project was to evaluate whether heavy trucks typically travel at significantly different operating speeds than passenger vehicles and what impact differences in on-road speeds would have on emissions. Average speeds and spot speeds were collected for heavy trucks and passenger vehicles for four arterial segments and spot speeds were collected for two freeway segments in Des Moines, Iowa. Average and spot speeds were collected for four arterial segments and three freeway segments in the Minneapolis/St. Paul, Minnesota metropolitan area. The results of this research show that heavy trucks and passenger vehicles operate differently on the road. Average and spot speeds were compared for heavy trucks and passenger vehicles by facility. Average and spot speeds for heavy-duty trucks were lower than for passenger vehicles for all locations. Differences could have consequences for project level and regional emissions modeling particularly since the ability to demonstrate conformity is based on the ability to correctly estimate and model vehicle activity

Toolbox to Assess Tradeoffs between Safety, Operations, and Air Quality for Intersection and Access Management Strategies

Significant transportation agency resources are allocated to meet maintenance, operations, safety, and air quality goals. Although there is a significant amount of overlap between these areas, decisions to meet agency goals in one area often do not consider goals in the others and, as a result, miss opportunities to leverage funds and make better informed decisions overall. There are a number of areas of overlap between capital improvements designed to improve operations, maintenance, safety, and air quality goals that provide a rich opportunity to leverage funds and use resources more cost-effectively while meeting agency goals in two or more of the areas. The objective of this research is to develop analytical tools that can efficiently evaluate common capital projects used to meet agency goals in one area (operations, safety, air quality, and maintenance) but that also have a significant impact on the others

Quantifying safety and speed data for rural roundabouts with high-speed approaches

If transportation agencies are going to move Towards Zero Deaths on their roadways, it will be essential to address the thousands of fatal and injury crashes occurring at intersections. With nearly 3,000 fatalities at rural intersections annually, better intersection designs are critical. Roundabouts are a proven safety countermeasure, but until this point the safety data for rural roundabouts on high speed roadways has been limited. This research conducted an in depth safety and approach speed data analysis for rural roundabouts on high speed roadways and provides the first published planning level crash prediction model available for rural roundabouts. Crash analysis results showed that rural roundabouts with high speed approaches significantly reduced total crashes by 62 to 68 % and injury crashes by 85 to 88 % at nineteen rural roundabouts. Moreover, the number of angle crashes, which tend to have a higher likelihood of causing injuries at high speeds, were reduced by 83%, also a statistically significant reduction. Approach speed data proved that drivers are able to slow down in advance of roundabouts on rural roadways and the mean speeds at 100 ft from the yield line were 2.5 mph lower than mean speeds at 100 ft from the stop bar at stop controlled approaches. Additionally, a comparison between roundabout approaches with and without rumble strips showed mean speeds 4.3 mph and 3.3 mph lower at 100 ft and 250 ft from the yield line, respectively, for the approaches with rumble strips; however, the variation in speeds increased with the introduction of rumble strips. The results of this research support decision-making to invest in an intersection alternative that lowers speeds and significantly reduces the risk of injury crashes. Roundabouts eradicate the risk of drivers running stop signs and red lights. Roundabouts save lives.</p

EVALUATING SPEED DIFFERENCES BETWEEN PASSENGER VEHICLES AND HEAVY TRUCKS FOR TRANSPORTATION-RELATED EMISSION MODELING

Heavy vehicles emit emissions at different rates than passenger vehicles. They may behave differently on the road as well, yet they are often treated similarly to passenger vehicles in emissions modeling. Although not frequently considered in calculating emission rates, differences in the operating speeds of passenger vehicles and heavy trucks may influence emissions. The main goal of this research project was to evaluate whether heavy trucks typically travel at significantly different operating speeds than passenger vehicles and what impact differences in on-road speeds would have on emissions. Average speeds and spot speeds were collected for heavy trucks and passenger vehicles for four arterial segments and spot speeds were collected for two freeway segments in Des Moines, Iowa. Average and spot speeds were collected for four arterial segments and three freeway segments in the Minneapolis/St. Paul, Minnesota metropolitan area. The results of this research show that heavy trucks and passenger vehicles operate differently on the road. Average and spot speeds were compared for heavy trucks and passenger vehicles by facility. Average and spot speeds for heavy-duty trucks were lower than for passenger vehicles for all locations. Differences could have consequences for project level and regional emissions modeling particularly since the ability to demonstrate conformity is based on the ability to correctly estimate and model vehicle activity.</p

Toolbox to Assess Tradeoffs between Safety, Operations, and Air Quality for Intersection and Access Management Strategies

Significant transportation agency resources are allocated to meet maintenance, operations, safety, and air quality goals. Although there is a significant amount of overlap between these areas, decisions to meet agency goals in one area often do not consider goals in the others and, as a result, miss opportunities to leverage funds and make better informed decisions overall. There are a number of areas of overlap between capital improvements designed to improve operations, maintenance, safety, and air quality goals that provide a rich opportunity to leverage funds and use resources more cost-effectively while meeting agency goals in two or more of the areas. The objective of this research is to develop analytical tools that can efficiently evaluate common capital projects used to meet agency goals in one area (operations, safety, air quality, and maintenance) but that also have a significant impact on the others.For more on this project and other project reports from InTrans, please visit http://www.intrans.iastate.edu/ </p