|Shouldering the problem
|The English Highways Agency is to follow in the footsteps of the Americans, the Dutch and a number of other countries in the routine use of hard shoulders as normal 'running' lanes. Although part of a wider Active Traffic Management scheme that will include a controlled motorway system and ramp metering, it is the issue of hard shoulder running (HSR) that is causing the greatest level of controversy.
Issues of safety and the access of the emergency services to incidents on the motorway, are frequently being raised in opposition to the idea of HSR and it is argued that introducing another lane will, far from relieving congestion, simply attract more traffic. Is there any basis for these arguments? And what is the business case for the introduction of HSR?
In all parts of the world where hard shoulder running has been introduced, the motivation has, with minor variations, been the same; an attempt to solve the worsening and apparently intractable problem of congestion without the political and financial costs involved in any road-widening or road-building project. To what extent such projects have been successful, together with the lessons that have been learned, is the subject of this article.
The principle is not new. The use of the hard shoulder as a running-lane has been routine in the United States for at least the past 10 years. In Virginia, its introduction followed the decision by the Virginia DOT to dedicate the offside lane of Interstate 66 as a high-occupancy vehicle (HOV) lane, effectively squeezing the remaining traffic into what was left of the road surface. And there are at least another half-dozen locations throughout the US where the highway authorities now make use of the additional lane to relieve congestion at particular times of the day. In the Netherlands, where the problem was high demand and low capacity, the idea of HSR has been under active consideration for about seven years and there are plans to extend its use from the current 25 Km to around 150 Km over the next 3-4 years. In Germany, the two sites presently utilising HSR are intended to allow drivers the option of leaving the motorway early.
In all three countries, there is anecdotal evidence of popular support for the local schemes, in spite of initial opposition in the press. Research by the highway authorities concerned has also shown improved traffic flows and, at least in the case of The Netherlands and Germany, to have led to a reduction in collisions.
"When we first thought about hard shoulder running," said Jim Robinson an Assistant Division Administrator with the Mobility Management Division of the Virginia DOT, "we faced a certain amount of opposition from motoring organisations and the press who were concerned that the idea might be dangerous to drivers. They have pretty much come around now. It has certainly added capacity and improved traffic flow."
But the apparent success of the principle of HSR has to be viewed in the context of its supporting systems including advanced traffic management systems to regulate the opening and closing of the use of the hard shoulder and to enforce compliance.
"We tried," said Robinson, "to use the idea (of HSR) on Interstate 99 without proper signs or other support services but we experienced an increase in crashes involving vehicles on the hard shoulder. We also had problems on the approaches to the ramps with drivers joining the hard shoulder too early. The lesson we learned was that you can't allow the use of hard shoulder running without adequate controls in place."
On Interstate 66, a high-speed, four lane freeway into Washington DC and on Interstate 264 in the Hampton Roads area of Virginia, the lessons of Interstate 99 have been learned and both routes have in place VMS (Variable Message Signs) and CCTV surveillance cameras. In addition to these, refuge areas have been built every 500 or so metres for the emergency use of drivers.
"There are differences in the management of the two freeways," said Staphany Hanshaw, manager of the Freeway Management System for the Hampton Roads Region of Virginia, "but as we gain experience, we are adding systems to improve safety and compliance levels."
Amongst these improvements is the provision of VMS over the affected section of hard shoulder of Interstate 66, together with an LED (Light Emitting Diode) sign showing either a large red cross (when the shoulder is closed) or a green arrow (when it is open).
"We have found the LED signs to be particularly effective," said Robinson, "although we still get the occasional violator. At the moment the hard shoulder becomes available for use at a fixed time every weekday on Interstate 66 but with the introduction of VMS and inductive loops to measure the traffic flow, this is likely to alter in line with the more advanced systems on Interstate 264."
In The Netherlands, the Dutch began using HSR on a short section of the A28 motorway outside Utrecht and it rapidly became evident that in addition to improving traffic flows during periods of high demand, the scheme was also resulting in a reduction in the number of collisions. To the surprise of the Dutch ministry of Transport, the drop in the collision rate was not confined to the A28 but extended to the surrounding, non-motorway routes where the free flowing traffic was less prone to rear-end shunts.
Like the Americans, the Dutch use HSR to avoid congestion but instead of allowing drivers to use the hard shoulder on a regular basis during peak hours, have limited its use to those occasions when congestion is unusually heavy. Computer software linked to induction loops in the carriageway determines when the system is turned on and off based on a pre-determined level of traffic flow. In effect this tends to mean three to four hours on almost every working day, resulting in a saving of about 10 minutes in the average journey time.
At all seven locations in The Netherlands where HSR is presently permitted, emergency refuge areas have been built at 500 metre intervals and equipped with MIDAS (Motorway Incident Detection and Automatic Signalling) inductive loops in addition to the traditional telephone linked to the control room. When a vehicle's presence is detected by the MIDAS loops, an automatic alarm warns the control room operator and pans the nearest CCTV camera onto the scene. Other safety features include a strictly enforced speed limit on the hard shoulder and a restriction on overtaking.
The system is, with minor variations, similar to that which the English Highways Agency is planning for a 16 Km (20 mile) section of the M42, south of Birmingham, as part of its £38 million (52.78 million Euro) Active Traffic Management for the area. The scheme will, according to David Arrowsmith, the Highways Agency engineer responsible for the initial delivery of the English system, provide upto 25% increased capacity at times of congestion, at minimal cost, and be unlikely to attract the additional traffic normally associated with new-build projects.
"Because there is no way of knowing, in advance, whether or not the hard shoulder will be available, the theory is that no additional traffic will be attracted to the motorway in consequence of HSR," said Arrowsmith. "This has been the experience of the Dutch and we are doing our own traffic modelling which is expected to support that view."
Yet the potential for collisions still remains with drivers expected to exercise a high degree of discipline and self restraint at times of acute congestion. The English system will not allow drivers to use the hard shoulder on the approach to an exit unless he/she intends to leave the motorway. Signs up to one and a half miles before the junction will direct through traffic to join the 'normal' running lane. But if traffic is already congested, the temptation will be to remain on the hard shoulder for as long as possible, even at the risk of inconveniencing drivers wishing to leave the motorway.
Perhaps for this reason, the Germans have restricted their own HSR trials in Lower Saxony, to the approaches to exit ramps. Drivers wishing to leave the A7 at the Gottingen interchange or the A1 at Holdorf are given the option of using the hard shoulder for up to 1000 meters before the ramp. Access to the shoulder is indicated by roadside signing which, in the case of the A7 is static and in the case of the A1, dynamic. In common with the Dutch experience, the Germans found a slight decrease in the total number of collisions since the installation of the system.
But while road safety is an important determinant in any decision about the use of HSR as a tool of traffic management, achieving an improved flow of traffic appears to be at least as high a priority in the minds of traffic engineers. At the same time, there is a sombre realisation that increasing traffic levels will soon erode the additional capacity that HSR provides and some other means of improving traffic flow will have to be found. Already being piloted in The Netherlands is the idea of an additional, narrow, outside lane that could be taken into use during periods of high demand. So too is the idea of a national traffic control centre which has been in operation in Holland since 1999 and is due to be copied in the UK next year.
"It is important that we are able to demonstrate the value of the systems we put in place," said Arrowsmith, speaking about the English pilot. "If we can't do that, then there would be no point in introducing the idea in the first place. Any new system needs to be effective in reducing congestion and improving traffic flow, in safety. The ATM pilot that is due to begin next summer will demonstrate whether or not there is a business case for each aspect of ATM. Until the pilot has been completed, we simply don't know although the signs are good. "
|For further information, visit:|
Jim Robinson at Virginia DOT, Tel: #1 804 786 6677, E-mail: firstname.lastname@example.org
David Grant, Project Sponsor or Simon Kirby, Delivery Sponsor both of the Highways Agency. E-mail: M42ATMProject@highways.gsi.gov.uk
Prof Bernhard Friedrich of the Institute of Transport Engineering and Planning, Hannover University. E-mail: Friedrich@ivh.uni.hanover.de