Design Guidelines
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Asian Highway Network Design Standard for Road Safety Infrastructure Facilities - Design Guidelines ASIAN HIGHWAY DESIGN STANDARD FOR ROAD SAFETY INFRASTRUCTURE AND FACILITIES DESIGN GUIDELINES 2nd DRAFT 6 August 2017 Asian Highway Network Design Standard for Road Safety Infrastructure Facilities - Design Guidelines CONTENTS PART 1 ROAD NETWORK PART 2 ROAD INFRASTRUCTURE PART 3 INTERSECTIONS PART 4 ROADSIDE SAFETY PART 5 PEDESTRIANS, SLOW VEHICLES AND TRAFFIC CALMING PART 6 DELINEATION, PAVEMENT MARKINGS AND LIGHTING PART 7 ROAD SIGNAGE PART 8 TUNNELS LIST OF REFERENCES Asian Highway Network Design Standard for Road Safety Infrastructure Facilities - Design Guidelines PART 1 ROAD NETWORK 1 GENERAL CONSIDERATIONS 1.1 Network Development 1.2 Interfaces 1.3 Transition Zones 2 SPEED LIMITS 2.1 General Considerations 2.2 Setting Speed limits 1 Asian Highway Network Design Standard for Road Safety Infrastructure Facilities - Design Guidelines 1 GENERAL CONSIDERATIONS 1.1 NETWORK DEVELOPMENT The Asian Highway Network consists of a diversity of road sections and facilities serving a variety of destinations of importance in population, industrial activities, tourism, logistics and international cross- border transport. The overall picture is illustrated in Fig. 1.1.1.1, Fig. 1.1.1.2 and Fig. 1.1.1.3. These road network and usage perspectives are fundamental considerations for road safety. Fig. 1.1.1.1 General Components of the Road Network Fig. 1.1.1.2 Major Bypasses Fig. 1.1.1.3 Key Facilities and Connections 1 Asian Highway Network Design Standard for Road Safety Infrastructure Facilities - Design Guidelines Signing of Expressways and Express Roads Access-controlled roads are preferably signed as expressways or express roads which are defined in national law for the exclusive use of motor vehicles. Expressways are appropriate for high standard primary roads with design speed not less than 80km/h. Express roads are appropriate for other access-controlled roads with design speed not less than 60km/h. The entrance and termination of expressways and express roads should be demarcated by traffic signs as shown in Fig. 1.1.1.4. The entrance traffic sign may also be embedded onto directional signs in the general road network leading to expressways or express roads. Fig. 1.1.1.4 Expressway and Express Road Symbols Bypass of Population Centers Bypasses are diversion routes which bring main road traffic away from built-up Areas. They are often beneficial around cities from the safety, environmental and urban design perspectives. Bypasses are also highly desirable around smaller built-up areas with thriving activities or narrow cross-sections of the road. City bypasses are preferably ring road systems, but they may also directly traverse urban areas in the form of expressways or express roads in tunnels, viaducts or flyovers. On the other hand, high priority corridors may follow entirely independent corridors and connected to cities via linkages. Where a bypass is not access-controlled, the number of intersections and direct frontage accesses should be restricted. Adequate right-of-way will be needed for future upgrading including widening, provision of service roads, grade-separated intersections and crossing facilities. Allowance for Future Widening In the design of new primary roads, adequate consideration should be given to the need for future widening. There are two possibilities: • Acquiring right-of-way to accommodate additional traffic lanes • Initial construction of one carriageway only for two-way traffic For Option 1, symmetrical widening is preferred as asymmetrical widening is generally more prone to safety problems during construction. Option 2 should not be adopted unless a high level of safety design and management is ensured. Special treatments are required to reduce the risk of indiscriminate overtaking and drivers’ misinterpretation as a unidirectional road. It is generally not recommended to construct only one tunnel tube of a planned twin tube tunnel for bidirectional traffic in the interim period. If this option is chosen, special measures will be required to minimize any safety risks. 2 Asian Highway Network Design Standard for Road Safety Infrastructure Facilities - Design Guidelines Network for Pedestrians and Slow Vehicles Mixed traffic of different types, masses and speeds on highways is prone to safety problems. Safety improvements on Asian Highway routes should, as far as possible, involve a wider optimization of the road network by diverting pedestrians and slow vehicles to local roads and minor corridors away from the main highway. Outside built-up areas, exposure of pedestrians, local traffic and slow vehicles to highway traffic should be minimized with a network strategy comprising one or more of the following measures: • Restricting the number of at-grade intersections and direct frontage accesses • Providing alternative or parallel routes or service roads • Grade-separation with or without intersection Re-use of Old Roads Where improvements of existing Asian Highway routes involve realignment, considerations should be given to the beneficial re-use of abandoned sections of the existing roads. Such re-use is preferably part of a network strategy to improve safety for pedestrians and slow vehicles. Possible initiatives include: • Existing road promoted as a local access road with traffic calming if the new road follows an entirely new alignment • Existing sections of roads and bridges parallel to the new road converted for the better use of pedestrians, slow vehicles or tourist traffic • New usage such as public parks, viewpoints, roadside parking areas, rest areas, emergency parking areas or bus stops Re-use of old bridges should be encouraged provided that they are well maintained. An individual old bridge only benefits one direction of travel, in which case pedestrian and slow vehicle facilities are still required for the other direction of travel. For successful re-use of existing roads, attention should be given to details so that they are attractive to users. It is generally desirable for users to be within the visibility of the new road for reasons of personal security. Intersections between the existing road and the new road should be minimized and treated with appropriate safety measures, particularly where crossing movements are expected. They should intersect the main road at right angle and are located on straight sections with adequate visibility. Where a bypass is available, the original urbanized section is preferably converted as a multi-purpose urban main street with traffic calming and pleasant streetscape in favor of pedestrians, slow vehicles and local activities. Intersections between the bypass and the existing road should be designed to clearly distinguish the bypass and the old road. 3 Asian Highway Network Design Standard for Road Safety Infrastructure Facilities - Design Guidelines 1.2 Interfaces General Requirements Phased improvements of Asian Highway routes will result in interfaces between road sections of different characteristics. Typical interfaces are illustrated in Fig. 1.1.1.4 Fig. 1.1.1.4 Typical Interfaces At the interface between road improvement projects and existing roads, particular attention should be given to road safety in the direction from the new road to the existing road. The following treatments may be applied to incite drivers adapting their speeds and behavior: • Cross-section change in conjunction with changes in the surrounding environment and landscape • Provision of roundabouts • Mandatory exit through slip roads of grade-separated intersections Interface areas should not be located where the existing road geometry is significantly inferior to the new road. Unfavorable situations include the presence of sharp curves, significant crest profiles, complex road environment, constrained visibility etc. Roadsides at interfaces should conform to good practices pertaining to clear zones and vehicle restraint systems. 4 Asian Highway Network Design Standard for Road Safety Infrastructure Facilities - Design Guidelines 1.3 Transition Zones Transition zones are road sections at the interface between different road classes, road types or road sections with different design speeds. These zones should be accompanied by physical changes of the road which are obvious and explicit, but not to the extent of causing abrupt braking. A change of speed limit at transition zones should accord with: • changes in horizontal and vertical alignment, cross-sections etc • interchanges, roundabouts, intersections which create a gateway effect • changes between urban and rural settings • different streetscape, plantings or landscape, safety barriers etc The length of transition zones may be based on a deceleration rate of 0.8m/s2 and is generally in the order of 100m to 200m for each stepwise speed limit reduction of 20km/h. Where speed limit is reduced by more than 30km/h, stepwise reduction of 20km/h or 30km/h is recommended. Termination of Primary Roads Special treatments are required at transition zones to alert drivers and to assist them adapting to the change where a primary road or access-controlled Class I road terminates in one of the following arrangements: • A lower design speed is adopted on the road • The primary road becomes a Class I road • The road becomes a Class II or Class III road • The road terminates directly onto an at-grade intersection • The road terminates at a partially constructed grade-separated intersection “End of Expressway” signs should be erected