The national standard "Code for Design of Urban Road Traffic Facilities" stipulates: When there is no median and there is no defense against the guardrail, the median should be set up; The Guide for Setting Traffic Fences on Urban Roads stipulates that when there is no central separation zone on urban two-way six-lane and above trunk roads, a central separation fence should be set up; In the middle of the road has been equipped with green isolation belt or cement isolation pier and other central separation zone of the road, when pedestrians and non-motor vehicles cross the motor vehicle lane seriously, a central isolation fence should be set up on the central separation zone.

However, in recent years, due to the unreasonable setting of isolation railings in some cities, traffic accidents that vehicles hit isolation railings and even collide with opposite vehicles have occurred from time to time. Therefore, it is necessary to further optimize the traffic safety of highway isolation belts in some cities.

1. Main traffic problems in the central isolation belt of main roads.

(1) The isolation belt is too narrow, and the isolation railing base invades the double yellow line.

The investigation shows that the central isolation belt of most main roads is generally narrow, and the double yellow line is only 50cm wide. There is a common double yellow line at the base of the isolation railing. Invasion of the carriageway building clearance does not meet the requirements of the Code for Design of Urban Road Routes for the width of kerbs.

The railing base is set on the double yellow line, which leads to the insufficient lateral clear distance of the motor vehicle lane, which is easy to cause the driver's avoidance effect, away from the median railing, deviating from the current lane and even entering the adjacent lane. At the same time, the line pressing vehicle can easily hit the base of the isolation railing, causing the railing to roll over, and the vehicle running at high speed is also easy to roll over.

(2) Inadequate warning guidance of isolation belt may easily lead to misjudgment by drivers.

The reflective film is generally located in the railing of the central isolation belt of some main roads, with a low position and a small area, which is insufficient in continuity and consistency, and it is difficult for remote drivers to identify and see the outline of obstacles clearly.

At the same time, the long-distance railings are not attractive, and the road alignment can't be seen clearly. Some railings have black and cyan bases and columns, which are not enough color difference with the road surface, low retroreflection coefficient, and are not easily perceived by drivers in low illumination. At the same time, the lack of anti-glare facilities and other facilities easily reduces the driver's ability to respond to changes in the surrounding environment of the road, causing misjudgment by drivers and potential traffic safety hazards.

(3) In the disaster climate, the significance is insufficient, and it is difficult to achieve full-time security.

The double yellow line of the central isolation belt of the main road is generally short of line-of-sight inducing and isolating facilities such as protruding road signs and elastic traffic posts, and the visibility is poor. In the case of low illumination and disaster climate (snow and rain), the line-of-sight is poor, and it is also easy to cause accidents such as vehicles entering the opposite lane by mistake and colliding.

2. Solutions to traffic problems in the central isolation belt of main roads.

(1) widen the median to meet the specification requirements.

The width of the existing median is increased to meet the requirements of various specifications. It is suggested that the width of the double yellow line of 50cm should be increased to 100cm and above, and the distance between the base of the isolation railing and the inner side of the double ring line should be increased to 16cm to meet the requirements of the Ministry of Public Security. If conditions permit, continuous high kerbs or short guardrails can be set in the median, and the marginal strip width should be ensured to be more than or equal to ≥25cm, so as to make the median more tolerant.

(2) Strengthen the warning induction of isolation railings to reduce the impact probability.

Facilities such as high warning posts and high upright posts are added at the end of the isolation railing in the central separation zone, and the high position setting is carried out to reduce the probability that the isolation railing and warning facilities are blocked, so as to ensure the visibility of the driver at the end of the isolation railing in a simple visual range.

Standardize the shape setting of the isolation railing. A strip-shaped reflective film can be set in the middle of the isolation railing to enhance contour induction and linear induction. The colors of the isolation railing base and the railing body should be high reflective colors such as white, orange (construction area) and yellow, so as to reduce the driver's misjudgment, reduce the collision probability and ensure driving safety.

(3) Add traffic facilities and build a number of guidance systems.

Traffic safety facilities such as protruding road signs and elastic traffic posts are added at the double yellow line of the central median (it is more necessary for the double yellow line of the central median without barriers), and the far end is visible, so as to enhance the visual reference system of the road surface, ensure the clear outline of the road under low illumination conditions and disaster conditions (rain, snow and ice climate), optimize the driver's sight distance and reduce the probability of traffic accidents.

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As an effective transportation facility, the central isolation belt separates the opposite lanes, improves the safety and order of driving, and improves the road traffic efficiency while ensuring traffic safety. Therefore, as a part of urban roads, the design and setting of the central isolation belt should be based on the perspectives of safety, smoothness, guarding traffic and pedestrian safety.