2+1-ROADS WITH AND WITHOUT CABLE BARRIERS: SPEED PERFORMANCE

The objective of this paper is to present the Swedish National Road Administration (SNRA) development program to upgrade traffic safety on existing 13 m cross-section roads using low cost measures and early findings on speed performance. Traffic safety findings have been reported in depth elsewhere. The main traffic safety proposal in the development program is conversion to 2+1 with a separating cable barrier and roadside improvements within existing right-of-way. In 1998, the director general of SNRA decided to proceed with a full-scale program with six sections. The empirical findings presented here are based on 1.5 years of experience from the first section to be opened, the E4 semi-motorway Gavle-Axmartavlan with an Annual Average Daily Traffic of 7000 veh/d; 2+1 partly with cable barrier partly only with road markings. The solution chosen on the first section gives one-lane sections with a total paved width of 5.6 m but only 4.6 at existing bridges and side guardrails. This has been heavily criticized as giving an unacceptable level-of-service for a national highway due to low overtaking opportunities and queues at vehicle breakdowns and maintenance operations. Early speed performance findings so far are as follows: the average car spot speed at speed limit 90 km/h has been 101 km/h; car spot speeds are in the range 93-100 km/h at the beginning of a one-lane section at traffic flows around 1200-1350 veh/h; 5% of the hourly speeds are below 90 km/h at speed limit 90 km/h; the 1% percentile speed at 90 km/h is 75 km/h at both the beginning of a one-lane and at the end of the two-lane location close to a transition zone; car spot speeds on overtaking lanes, 300-350 veh/d, are very high in the range 110-120 km/h, far above the official speed limit of 90 km/h (before April 1999); average passenger car spot speeds on two-lane sections are 4 km/h higher in September 1998 on the cable barrier section compared with September 1997 with wide lanes, and on two-lane sections with road marking the spot speeds are slightly higher than for the cable barrier section; passenger car speeds on one-lane sections on the cable barrier part are more or less unchanged though speeds at side steel barriers have decreased some km/h, and speeds on the road marking part seem to be approximately 2 km/h higher in one-lane sections; side cable barriers 1 m from the pavement do not affect speeds; there is approximately one median barrier repair per week requiring on average a 2 hour overtaking lane closure; two illegal transports, one with an over-width truck and one with an over-height truck, have been stuck resulting in long queues; and some five accidents and incidents have blocked one direction for numerous hours.

Language

  • English

Media Info

  • Features: Figures; Photos; References;
  • Pagination: p. 188-199
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00795379
  • Record Type: Publication
  • Report/Paper Numbers: E-C018
  • Files: TRIS, TRB
  • Created Date: Jul 25 2000 12:00AM