Criteria for roadside safety of motorways and express roads A proposalfor road authorities in the framework of the European research project SAFESTAR, Workpackage 1.2. D-99 -2 Chris Schoon Leidschendam, 1999 sway Institute for Road Safety Research, The Netherlands Report documentation Number: D-99-2 Title: Criteria for roadside safety of motorways and express roads Subtitle: A proposal for road authorities in the framework of the European research project SAFESTAR, Work package 1.2. Author(s)·. Chris Schoon Research manager: Theo J anssen Project manager: Atze Dijkstra Project number SWOY: 69.886 Project code client: Contract No. RO-96-SC.203 Client: This project was funded by the European Commission under the Transport RTD Programme of the Fourth Framework Programme. Keywords: Motorway, side, safety, safety fence, vehicle occupant, obstacle, collision, hard shoulder, safety drums (crash cushion), steel, concrete. Contents of the project: Safe roads ides and medians are important for the protection of occupants of vehicles that leave the road. This report describes how to make safe roadsides by means of obstacle-free zones, slopes, frangible poles, crash cushions and safety barriers. The research was aimed at defining criteria for locations where safety devices are necessary. The research contained a literature study on national European standards. Furthermore, results from a questionnaire, which was send to European institutes and ministries, are described. Data from European countries, but also from the United States were analysed to prepare a proposal for standards and strategies for EU-countries. Number of pages: 58 +4 pp. Price: Dfl.25,- Published by: SWOY, Leidschendam, 1999 SWOY Institute for Road Safety Research P.O. Box 1090 2260 BB Leidschendam The Netherlands Telephone 31703209323 Telefax 31703201261 Deliverable D 1.2 Criteria for roadside safety of motorways and express roads SAFESTAR Contract No. RO-96-SC.203 Project: Safety Standards for Road Design and Redesign Coordinator: SWOV Institute for Road Safety Research, Leidschendam NL Partners: TNO Human Factors Research Institute; Soesterberg, NL RD Road Directorate; Copenhagen, OK VTI Swedish Road and Transport Research Institute; Linkoping, S VTT Technical Research Centre of Finland; Espoo, FIN LNEC Laboratorio Nacional de Engenharia Civil; Lisbon, P NTUA National Technical University of Athens; Athens, GR CETE Centre d'Etudes Techniques de I'Equipement Normandie Centre; Grand-Quevil/y, F RC Transport Research Centre; Bmo, CZ PROJECT FUNDED BY THE EUROPEAN COMMISSION UNDER THE TRANSPORT RTD PROGRAMME OF THE FOURTH FRAMEWORK PROGRAMME Summary To protect occupants of vehicles that leave the road from serious injuries, safe roads ides and medians are important. This report describes the way to make safe roadsides by means of obstacle-free zones, slopes, frangible poles, crash cushions and safety barners. The research performed here aims to define criteria for places where safety devices are necessary. The research was carried out by means of a literature study including the national European standards. Furthermore, results from a questionnaire which was send to European institutes and ministries are described. This questionnaire contained for instance questions about national standards and/or criteria for use of safety barriers, and about accident data on motorways and express roads where safety barriers were involved. Data from European countries, but also from the United States were analysed to prepare a proposal for standards and strategies for EU-countries. The first issue of the report deals with the desirable width for the obstacle­ free zone. Figures are presented about the only European research carried out in the Netherlands in the 1980's. Figures for motorways, single-lane highways and local single-lanes are given. Based on the questionnaires, distances of obstacle-free zones from other European countries are mentioned. The second issue is a shoulder with safe slopes. Figures from the United States and European countries are discussed. The figures from the Nether­ lands are based on mathematical simulations and twelve full-scale tests on slopes with two gradients. If fixed objects are made to yield, the third issue, they can be placed in an obstacle-free zone without safety barriers. Different solutions are mentioned, such as slip base, plastic hinges, fracture elements or a combination of these. The fourth issue deals with crash cushions. If solitary rigid obstacles along a shoulder cannot be removed, they can be shielded with a crash cushion .Crash cushions are applied on motorways in mainly two different situations: in pointed areas at exits (often at the beginning of a safety barrier) and on shoulders to shield single objects. If crash cushions have been hit head 'On, be vehicle usually remains within the shoulder so that it forms no danger for other traffic. In the case of a side impact, most types of crash cushions function like a safety barrier. Several European countnes have their own, different types of crash cushions . In the concept of a safe road side (shoulders and medl~ms), protection With safety barriers is the least safe solution (the last issue). An effectively functioning safety barrier prevents a vehicle from leavI'ng the roadway and striking a fixed object or terrain feature that is considered more hazardous than the barrier itself. But a colliSion with a safety bamer is never free from the n"sk of injuries for the occupants of the colh'ding vehicle, nor is it for othe r road users. Requirements ,CEN standards, containment levels, differences between steel and concrete barriers, and Dutch expenences with mathema - tical simulations are described. 5 Proposals for motorway standards and strategies for EU countries are discussed. There are safety reasons for favouring wide obstacle-free zones. Based on infonnation from many European countries a minimum width of 9 metres is recommended. Also is recommended to carry out accident investi­ gations in different European countries to collect more data in order to take a more well-founded decision for the European situation. Slopes may be a part of an obstacle-free zone if vehicular manoeuvres are possible. This is the case with a gradient of at least 1:5 for high slopes (> 5 m) and 1:6 for lower slopes « 2 m). Only fixed roadside objects can be located within an obstacle-free zone, if their support poles are frangible. If solitary rigid obstacles can not be re ~ bcated, protecting them with a crash cushion is the solution. In the report a decision model is described for determining the choice for shoulders and the median: obstacle-free or safety barriers. If a decision is made for a low containment level, steel barriers are in favour if only the installation costs are calculated. Taking into account other aspects, it depends on the local circumstances which type of barrier is to be preferred. Differ­ ences between countries are too great for a general statement. Also for express roads and single carriageways recommendations are given for the width of obstacle-free zones and the necessity for safety barriers. The single carriageway roads are in fact at the heart of the problem of obstacle accidents in Europe. There are many of such accidents because there are so many old roads. Unfortunately, accidents with "natural" obstacles such as trees, are widely spread so that dealing with them cannot be targeted at concentrations of dangerous locations. Apart from the erection of safety barriers, the driving speeds will have to be drastically reduced to increase the safety of such roads. Subsequently, this means that the road's function will be changed. A procedure has been described for identifying the locations and establishing prioritles for those most requiring the placing of safety barriers. As a cost-benefit analysis, the "one million ECU test" of the European Commission can be applied. A strategy developed in Amenca to deal with these problems, appears to be applicable also in Europe. It concerns for instance better accident monitoring, research, more attention (education, spreading infonnation, good manage­ ment), and greater budgets. 6 Contents 1. Introduction 9 1. 1. Objectives 9 1.2 · Method 9 1.3. Interaction between the function, cnteria and standards concerning the roadside 10 1.3.1. Function 10 1.3.2. Criteria 10 1.3.3. Standards 10 2. Investigation by questionnaires to European countries 11 2.1. The questionnaire 11 2.2. Response 11 2.3. Results 12 3. Accident analyses 16 3.1. Injury accidents with safety barriers on motorways 16 3.2. Characteristics 18 3.2.1. Pre-crash 18 3.2.2. Characteristics of the off-the-road vehicle 18 3.2.3. Severity of collisions with obstac es 18 3.2.4. Input conditions tests safety barriers 19 3.3. Risk and models 20 4. Concept ofa safe roadside 23 4.1. Introduction 23 4.2. A shoulder without obstacles 23 4.3. A shoulder with safe slopes 28 4.4. Shoulder with fixed objects that yield easily upon collision 31 4.5. Shoulder with crash cushions 32 4.6. Shoulder with safety barriers 33 4.6.1. Introduction 33 4.6.2. Requirements 33 46.3 . CEN standards 34 46.4. Containment levels 34 4.6.5. Literature search into safety barriers at H4 leve I 35 4.6.6 . Experiences wIth mathematical simulations 35 4.6.7. New developments 37 5 . The difference between steel and concrete barriers 39 5.1. In general 39 5.2 · A French study 39 53 · A German study 39 54. An Austrian study 40 5.5. A Dutch study 40 5.6 · Results from the questIonnaires 40 51. DiSCUSSIon 41 7 6. Cost-effectiveness 42 6. 1. A meta-analyses 42 6.2. European studies 42 6.3. Studies in the United States 43 7. Strategies in the US for improving roadside safety 45 7.1. Problems and analysis 45 7.2.