Highways Agency - Safe roads, Reliable journeys, Informed travellers

M5 Junctions 19-20 (Naish Hill) Towing Vehicle Signing Trial

Introduction

The results of this pilot scheme, which was run by the Highways Agency on the M5 motorway near Bristol last summer, are now available. The scheme involved the trial of advisory lane restrictions for towing vehicles on the southbound carriageway at Naish Hill, a two-mile stretch of the M5 immediately south of Junction 19, where severe tailbacks are common during summer weekends.

Read the full report or read on for further background information.

Background Information

The M5 is a vital link to the South West for tourists but long queues regularly develop on bank holiday and summer weekends. These are caused partly by a short steep hill south of Bristol, known locally as Naish Hill, and can extend back beyond the M4/M5 interchange at Almondsbury, a distance of more than ten miles. The Highways Agency has identified that the permanent solution is a climbing lane, for which a contract was awarded earlier this year and is due to be completed by summer 2006.

The Highways Agency monitors traffic flow at this location by permanent traffic counters installed on Avonmouth Bridge. These counters are able to measure traffic flow and speed and distinguish between different vehicle types as well as those vehicles that are towing caravans and trailers. The data shows that the volume of towed vehicles on bank holiday and summer weekends is much higher, as much as four times, and average vehicle speeds are much lower than on normal weekends.

About The Trial

The priority lane trial set out to reduce congestion at Naish Hill near Bristol during the peak holiday period. Drivers towing trailers who switched lanes were seen as making conditions worse. Sudden lane changing causes other drivers to brake and this interrupts the smooth flow of traffic and contributes to the start of the queuing.

Following discussions with motoring and caravan organisations, drivers of towing vehicles were asked not to overtake on Naish Hill at peak periods and advisory lane restrictions were put in place on Friday afternoons and Saturday mornings during August 2004. A press release was issued and widely circulated advising drivers of the restrictions beforehand. Contrary to what was reported in the press, the restriction applied to all towing vehicles and not just to caravans.

Results of the Trial

A report produced evaluating the effectiveness of the trial found as follows:

• On average towing vehicles represented less than 2.5% of the total vehicle volume on Fridays 1200-2400hrs, and 4% on Saturdays 0600-1800hrs.
• Average lane use of the nearside lane by towing vehicles was 84% prior to the pilot signs being installed on 30 July. This increased slightly to 91% following installation of the pilot signs.
• The pilot signs may have encouraged more towing vehicles to use the nearside lane, but it did not appear to reduce the incidence of summer weekend traffic congestion on Naish hill.
• The flow of the traffic was often good even with high traffic volume, so the suggestion that higher volumes of towing vehicles (expressed as a percentage of all traffic) cause congestion may be false.
• One cause of congestion appeared to be cars tending to use the two outer lanes, possibly by drivers perceiving these lanes to be less congested when in fact their tendency to use these lanes may actually be the cause of congestion leading to stop-start conditions at the base of the hill; it was observed that stop/start conditions usually started in the outside lane and then migrated to the middle lane and finally the nearside lane.

Summary

The pilot signing study increased the proportion of towing vehicles using the nearside lane in preference to the middle lane. The result is encouraging but there are still nearly 1 in 10 vehicles with trailers using the middle lane.

The trial on Naish Hill did not result in the hoped-for reduction in the incidence, duration and extent of holiday period traffic congestion and long tailbacks remain a problem. Study of the closed circuit television recordings made during the trial has shown that a minority of other drivers are not showing proper consideration and have poor lane discipline.

The Highways Agency will continue to study the CCTV recordings made during the trial, which have given us valuable information on driver behaviour and on how tailbacks start, and will now look at how to tackle poor lane discipline by other drivers at this location.

For next summer, the Agency is looking at other measures to improve the conditions and these may include the advisory priority lane restrictions used this summer as part of a package of measures. At the same time work on building a new climbing lane at Naish Hill will continue with construction planned for later in 2005.

Contact Information

If you require any further information about this report or the trial itself, please telephone the Highways Agency Project Sponsor Stephen Coe on 0117 372 8878, or the Highways Agency Information Line on 08457 504030 or via e-mail at ha_info@highways.gsi.gov.uk.