MEDIAN TREATMENTSMediansMedian treatments for roadways represent one of the most effectivemeans to regulate access, but arealso the most controversial. The twomajor median treatments includetwo-way left turn lanes (TWLTL) andraised medians.The safety benefits of medianimprovements have been the subjectof numerous studies and syntheses.Studies of both particular corridorsand comparative research on different types of median treatments indicate the significant safety benefitsfrom access management techniques. According to an analysis of crash data in seven states, raised medians reducecrashes by over 40 percent in urban areas and over 60 percent in rural areas. [4]A study of corridors in several cities in Iowa found that two-way left-turn lanes reducedcrashes by as much as 70 percent, improved level of service by one full grade insome areas, and increased lane capacity by as much as 36 percent. [5]Raised medians also provide extra protection for pedestrians. A study of median treatments in Georgia found that raised medians reduced pedestrian-involved crashes by 45percent and fatalities by 78 percent, compared to two-way left-turn lanes. [12]

TURNING LANES

eft Turns

xclusive turning lanes for vehicles remove stopped vehicles from

hrough traffic. Left-turn lanes at intersections substantially reduce

ear-end crashes. A major synthesis of research on left-turn lanes

emonstrated that exclusive turn lanes reduce crashes between 18

o 77 percent (50 percent average) and reduce rear-end collisions

etween 60 and 88 percent. [4]

eft-turn lanes also substantially increase the capacity of many roadways. A shared left

urn and through lane has about 40 to 60 percent the capacity of a standard through

ne. [4]. A synthesis of research on this topic found a 25 percent increase in capacity,

n average, for roadways that added a left-turn lane. [13]

ndirect Turns

ome of the biggest issues with managing access come at intersections where vehicles

must cross traffic. Some states and cities have adopted indirect turns to reduce these

onflicts. In New Jersey, the jug-handle left turn requires a right turn onto a feeder

treet, followed by a left onto a cross street. Detroit has

xtensively used an indirect U-turn that requires a U-turn

ast an intersection, followed by a right turn instead of a

egular left turn.

ke dedicated left-turn

nes, indirect turns reduce

rashes, improve conges

on, and add capacity.

rashes decline by 20 per

ent on average, and 35

ercent if the indirect turn

tersection is signalized.

apacity typically shows a

5 to 20 percent gain. [4]

Right Turns

Right-turn lanes typically have a less substantial impact oncrashes and roadway capacity than other types of turnstrategies, because there are fewer limitations on rightturns. Though there are fewer studies of these impacts,there is a clear relationship between the number of vehiclesattempting a right turn in a through traffic lane and its delayto through traffic. This relationship is exponential – eachadditional car that must wait for a right turn will increase the

elay more than the previous car. At intersections with substantial right-turn movements, a dedicated right-turn lane segregates these cars from through traffic and

creases the capacity of the road.

Roundabouts

oundabouts represent a potential solution for inter

ections with many conflict points. Though not appro

riate for all situations, roundabouts reduce vehicle

movements across traffic. Only a few studies have

xamined the safety benefits of roundabouts. One

tudy of four intersections that were replaced with

oundabouts in Maryland found a drop in crashes

etween 18 and 29 percent and a reduction in injury

rashes between 63 and 88 percent. The cost ofrashes at these locations – one measure of severity

 was also reduced by 68 percent. Overall crashes

n roundabouts were more minor than those at left

urn locations. [9] Another study of roundabouts in

everal locations found a 51 percent reduction in

rashes, including a 73 percent reduction in injury

rashes and a 32 percent reduction in property-damage-only crashes for single-lane round

bouts. Multi-lane roundabouts only experienced a 29 percent reduction in crashes. [6]

Business ConcernsInstalling raised medians often raises serious concerns by the business communitythat local businesses that depend upon pass-by traffic (especially gas stations andfast-food restaurants [10]) will be adversely affected by medians. Though there arefew studies of the actual impacts of medians on business sales, there are several surveys of business owner opinions. Surveys conducted in multiple corridors in Texas, Iowa, and Florida demonstrate thatthe vast majority of business owners believe there have beenno declines in sales, with some believing there are actuallyimprovements in business sales. [2,5,8] One study in Texasindicated that corridors with access control improvementsexperienced an 18 percent increase in property values afterconstruction. [2]
CITATIONS

1] Colorado Department of Highways, 1985, Final Report of the Colorado Access Control

Demonstration Project, Colorado.

2] Eisele, W. E., and W. E. Frawley, 1999, A Methodology for Determining Economic

Impacts of Raised Medians: Data Analysis on Additional Case Studies, Research Report

3904-3, Texas Transportation Institute, College Station, Texas, October.

3] Frawley, W. E., and W. E. Eisele, 1998, A Methodology to Determine Economic Impacts

of Raised Medians on Adjacent Businesses, 1998 National Conference on AccessManagement.

4] Gluck, J., H. S. Levinson, and V. Stover, 1999, Impacts of Access Management

Techniques, NCHRP Report 420, Transportation Research Board.

5] Iowa Department of Transportation, 1997, Access Management Research and

Awareness Program: Phase II Report.

6] Jacquemart, G., 1998, Synthesis of Highway Practice 264: Modern Roundabout

Practice in the United States, National Cooperative Highway Research Program, National Academy Press, Washington, D.C.

7] Lall, B. K., D. Huntington, and A. Eghtedari, 1996, Access Management and Traffic

Safety, Paper presented at the Second Annual Access Management Conference.

8] Long, G, C.T. Gan, and B.S. Morrison. "Impacts of Selected Median and Access 

Design Features." Florida Department of Transportation Report, Transportation 

Research Center, University of Florida, May 1993.

9] Meyers, E. J., 1999, Accident Reduction with Roundabouts, Paper presented at the

69th Annual ITE Meeting, Las Vegas, Nevada.

10] Neuwirth, R. M., G. E. Weisbrod, and S. D. Decker. 1993, Methodology for Evaluation

Economic Impacts of Restricting Left Turns, Paper presented at the First Annual AccessManagement Conference.

11] Pant, P. D., M.D., S. Ula, and Y. Liu, 1998, Methodology for Assessing the Effectiveness

of Access Management Techniques, Final Report, prepared for the Ohio Department of

Transportation.

12] Parsonson, P. S., M. G. Waters III, and J. S. Fincher, 2000, Georgia Study Confirms the

Continuing Safety Advantage of Raised Medians Over Two-Way Left-Turn Lanes, presented at the Fourth National Conference on Access Management, Portland, Oregon.

13] S/K Transportation Consultants, Inc., 2000, National Highway Institute Course Number

133078: Access Management, Location, and Design, April.

14] Texas Transportation Institute, In Progress, An Evaluation of Strategies for Improving

Transportation Mobility and Energy Efficiency in Urban Areas, Texas A&M University,Project 60011.

FOR MORE INFORMATIONhttp://www.accessmanagement.govFHWA Document Number FHWA-OP-03-066