1. Lars H. Trandem and Kelly Pitera
TRADEOFFS BETWEEN A 2+1 LANE ROAD DESIGN AND A NARROW 2+2 LANE ROAD DESIGN
Lars H. Trandem and Kelly Pitera

2. Background
AADT: –
Speed Limit: 90 km/h

3. Background
AADT: –
Speed Limit: 100 km/h

4. Background
VS.

5. Tradeoffs
SAFETY
OPERATIONS
COST

6. COMPARATIVE L.O.S. ANALYSIS
Methods
LITERATURE REVIEW
COMPARATIVE L.O.S. ANALYSIS
CASE STUDY
BENEFIT COST ANALYSIS

7. 2+1 Lane Road Design
AADT:
Speed limit: 90 km/h

8. Narrow 2+2 Lane Road Design
AADT:
Speed limit: 90 km/h

9. Traffic Safety
Head-on Collisions  Median Barrier
Run-off-road Crashes  Lane and Shoulder Width
Lack of data

10. Traffic Safety Head-on Collisions Impact of a median barrier
Great success in Sweden with 2+1 lane roads
Reduced fatalities by 76%
Applicable for both designs
Carlsson, A. (2009). Evaluation of 2+1-roads with cable barriers: final report

11. Traffic Safety Run-off-road Crashes Sufficient Clear Zone
Lane and Shoulder Width
Studies have shown narrower shoulder and lanes results in higher accident frequencies
Bauer, K. M., Harwood, D. W., Hughes, W. E., & Richard, K. R. (2004). Safety Effects of Narrow Lanes and Shoulder-Use Lanes to Increase Capacity of Urban Freeways.
Dixon, K., Fitzpatrick, K., & Avelar, R. (2015). Operational and Safety Tradeoffs -- Reducing Freeway Lane and Shoulder Width to Permit an Additional Lane.

12. Traffic Safety Summary Hard to separate the effects
Wider lanes and shoulders are favorable
2+1-road assumed to be safer

13. Traffic Operations Capacity Level of Service
(US) Highway Capacity Manual

14. Traffic Operations Studies have shown:
Capacity of 2+1 lane road is around veh/h for one direction
Compared to 1900 veh/h for 1+1 lane road
A 2+1 lane road does not improve the capacity of a 1+1 lane road
But 2+1-roads improve the level of service
Multilane highway segments have a capacity of – veh/h/l
Narrow 2+2 lane roads improve capacity and level of service
Carlsson, A. (2009). Evaluation of 2+1-roads with cable barriers: final report
Transportation Research Board. (2010). Highway Capacity Manual 2010

15. Level of Service Calculations
Traffic Operations
Level of Service Calculations
Highway Capacity Manual
Basic freeway segments (narrow 2+2 road)
Adapted two-lane highway method (2+1 road)
AADT: 6 000, and
Directional splits: 67/33 and 55/45

16. Level of Service Calculations
Traffic Operations
Level of Service Calculations
Level of Service
Directional split
AADT
2+1 Lane road
Narrow 2+2 Lane Road
67/33
6 000 C A
12 000 B
20 000 -
55/45
12 000

17. Norwegian Case Study E16 Kløfta-Kongsvinger
Benefit Cost Analysis
 Non-monetized
 Monetized

18. Non-monetized Impacts
Norwegian Case Study
Non-monetized Impacts
Landscape
Local surroundings and outdoor activities
Biodiversity
Cultural environment
Natural resources

19. Norwegian Case Study Monetized Impacts
Benefit-cost analysis by using the program EFFEKT
Alternative 0 (existing situation)
Alternative 1 (narrow 2+2 road)
Alternative 2 (2+1 road)

20. Norwegian Case Study Scenario 1
Speed Limit: 90 km/h for both alternatives
Road design
Accident types that are affected
Killed
Seriously injured
Lightly injured
Number of accidents
Narrow 2+2-road (Alt. 1)
All
-75%
-45%
+25%
2+1-road (Alt. 2)
-76%
-47%
+13%

21. Norwegian Case Study Scenario 2
Speed Limit: - 90 km/h for narrow 2+2 road (Alt.1) - 85km/h for 2+1 road (Alt.2)
Traffic accident effects as in Scenario 1

22. Norwegian Case Study Scenario 3
Speed Limit: 90 km/h for both alternatives
Traffic accident effects assumed equal for both narrow 2+2 road (Alt. 1) and 2+1 road (Alt. 2).

23. Scenario 1 Scenario 2 Scenario 3
Scenario 1
Scenario 2
Scenario 3
Components
Alt. 1 (2+2)
Alt. 2 (2+1)
Alt.1 (2+2)
Alt.2 (2+1)
Investment cost [ 1000 NOK]
(-)
Change in time cost [1000 NOK]
1 033 775
(+)
873 290
658 631
Change in Accident costs [1000 NOK]
394 703
416 022
416 028
Change in additional miscellaneous costs and benefits [1000 NOK]
174
100 915
160 448
Net present value [1000 NOK]
607 016
651 069
495 942
628 341
Benefit-cost ratio per budget kroner [ ]
1,65
1,82
1,28
1,71

24. Scenario 1 Scenario 2 Scenario 3
Scenario 1
Scenario 2
Scenario 3
Components
Alt. 1 (2+2)
Alt. 2 (2+1)
Alt.1 (2+2)
Alt.2 (2+1)
Investment cost [ 1000 NOK]
(-)
Change in time cost [1000 NOK]
1 033 775
(+)
873 290
658 631
Change in Accident costs [1000 NOK]
394 703
416 022
416 028
Change in additional miscellaneous costs and benefits [1000 NOK]
174
100 915
160 448
Net present value [1000 NOK]
607 016
651 069
495 942
628 341
Benefit-cost ratio per budget kroner [ ]
1,65
1,82
1,28
1,71

25. Scenario 1 Scenario 2 Scenario 3
Scenario 1
Scenario 2
Scenario 3
Components
Alt. 1 (2+2)
Alt. 2 (2+1)
Alt.1 (2+2)
Alt.2 (2+1)
Investment cost [ 1000 NOK]
(-)
Change in time cost [1000 NOK]
1 033 775
(+)
873 290
658 631
Change in Accident costs [1000 NOK]
394 703
416 022
416 028
Change in additional miscellaneous costs and benefits [1000 NOK]
174
100 915
160 448
Net present value [1000 NOK]
607 016
651 069
495 942
628 341
Benefit-cost ratio per budget kroner [ ]
1,65
1,82
1,28
1,71

26. Case Study Monetized Impacts
Conclusion
Case Study Monetized Impacts
Which design is most economical beneficial? - It depends……

27. Conclusion Traffic Safety Both designs improve the traffic safety
Assuming a slight advantage to the 2+1 lane road - wider lanes and shoulders - assumed lower mean speed

28. Conclusion Traffic Operations
2+1 lane road - No increase in capacity - Improved level of service
Narrow 2+2 lane road - Increase in capacity - Improved level of service

29. Final Conclusions 2+1 with certain volume conditions
Need for more data