Lecture: Mr. Kuang Zixian, consultant of road safety and traffic engineering in Hong Kong.
Topic of this issue: How to reduce traffic accidents through road safety engineering and evaluation?
What I want to talk to you today is the concept of road safety engineering and road safety audit. In Europe and Hong Kong, the concept of road safety assessment is only used for new roads and reconstruction projects, and the methods of road safety investigation and accident data analysis are used for existing roads. However, both road safety review and safety inspection are just a procedure. The most important thing is to establish and improve the technical foundation of road safety engineering.
What are the common faults of first-class highways and second-class highways?
There are many fatal accidents caused by side collision of first-class highway and frontal collision of second-class highway.
No matter whether it is a first-class highway or a second-class highway, a third-class highway or a fourth-class highway, it is necessary to fully understand the accidents and problems before giving useful suggestions. I made a correlation analysis on the accident data of a province in China. According to many accident data, side collision is the main problem of first-class highway fatalities, while frontal collision is the main problem of second-class highway fatalities. This is because many first-class highways have defects in road design, especially in grade crossing. There are often cases of forced overtaking and speeding on secondary roads.
▲ Figure: The secondary road forcibly overtakes.
The strategy of overtaking facilities along expressway can effectively reduce the risk of frontal collision.
For example, a two-lane expressway needs to consider whether to provide enough overtaking opportunities for drivers. On the second-class highway, if there is a big truck with a speed of 30 kilometers per hour in front, the driver behind will drive to the opposite lane to overtake at the first time, but whether it is safe or not depends on whether there is enough overtaking sight distance and traffic gap. However, many secondary roads in mountainous and hilly areas cannot provide enough overtaking sight distance due to route design. In fact, there are many safer overtaking facilities, including climbing lanes, partially separated sections and roadside parking spaces. ...
Second, how to reduce traffic accidents from the perspective of road safety engineering?
First-class roads crossing villages and towns: Before crossing villages and towns, the nature and form of roads need to be effectively changed.
The first-class highway is a kind of highway form between expressway and ordinary highway, which covers the characteristics of expressway and ordinary highway. Because of the high speed and multi-lanes, there are hidden dangers when passing through villages and towns. So how to handle it safely?
Drivers driving through villages and towns on the first-class highway will bring great danger to pedestrians and non-motor vehicles in villages and towns if the shape and environment of the road ahead have not changed and they can't see any deceleration instructions. Therefore, when the first-class highway must pass through villages and towns, only by effectively changing the nature and shape of the highway and setting up enough safety facilities can the driver's behavior be changed.
No signal level crossing: Set a left turn lane.
It is necessary to set up a left-turn lane at an unsignalized intersection. At present, left-turn lanes are generally only set on urban roads. If you want to turn left on the secondary and tertiary roads, you need to turn left directly from the driveway. Setting a left-turn lane on expressway can provide a safe waiting space for left-turn vehicles, and prompt drivers to slow down and drive slowly before turning, which can not only effectively reduce side collision accidents, but also reduce the incidence of rear-end collisions.
▲ Figure: Left turn lane at signalless intersection. (Source: Google Street View)
There are two ways to set up a left-turn lane: one is to mark the lane, and the other is to set up a traffic island. When setting the left-turn lane, it is also allowed to reduce the lane width (for example, the original lane is 3.75 meters, which can be reduced to 3.5 meters or even 3 meters), thus reducing the need to widen the subgrade.
First-class highway: Widening the median can reduce the risk of side collision.
▲ Figure: Widening the central divider of the first-class highway. (Source: British Road and Bridge Design Manual TD42/95)
The recent traffic accident in Inner Mongolia happened on the first-class highway. The median of this highway has not been widened. Vehicles should turn left or cross the road, either pass quickly or stop halfway. If you park in the middle, even a 6-meter-long car will go beyond the 3-meter-wide median and block the main lane. Therefore, some countries widen the median to 10 meter to effectively accommodate most vehicles (including most trucks) and make them turn left or cross gradually.
Secondary highway: Widening the center line can reduce the risk of frontal collision.
Drawing a widened center line on the secondary highway can increase the lateral distance of the opposite vehicle, which can not only reduce the collision risk, but also reduce improper overtaking behavior. In addition, while widening the center line, the lane width can be compressed to 3.25 meters or even 3 meters.
▲ Figure: Widened centerline on the secondary road.
The center line can also be widened on the curve. For example, the existing expressway has poor alignment and an S-shaped sharp bend, so it is necessary to straighten the alignment theoretically. However, in the case of limited funds and no damage to the environment, we can consider drawing a widened center line on the curve, and at the same time drawing a vibration marker before entering the curve to facilitate the driver to slow down and pass through the curve.
▲ Figure: Widened centerline on the curve. (Source: British Road and Bridge Design Manual TA85/0 1)
Third, reduce road traffic accidents and do a good job in road safety review.
Analyze the historical accident data and find out the similarities.
When doing accident analysis, we are most interested in seeing whether there are * * * the same factors or patterns in accidents in the same place or on the same road section. If there is no * * *, it is more difficult to solve the problem. The situation on the left in the picture below shows that most of the accidents occurred in the dark and the road surface was slippery, so we can put forward an improvement plan when dealing with it.
▲ Figure: According to the * * nature of "most accidents occur at night and the road surface slips", the targeted improvement scheme is put forward. (Source: Road safety.
If accidents often occur in a place or road section, it is necessary to find the similarities, present the problems in a simple form, and then summarize the problems for road designers to discuss.
Doing a good job of road safety review requires the cooperation of review team, design institute and owner.
Next, let's talk about road safety audit. Road safety assessment has been implemented for a long time in some countries and regions. For example, Britain began to implement the relevant system in 1988, while Hong Kong is still in its infancy.
Road safety review requires the joint efforts of three parties (review team, design institute and owner) to control safety risks at a reasonable and feasible level. When systematically evaluating the road design before opening to traffic, the evaluation team members have the responsibility to ask whether there are potential safety hazards and give feasible suggestions for improvement. The design institute needs to seriously consider adopting it. If the proposal is not adopted, it is necessary to write a report to clarify the reasons for not adopting it, or to propose an alternative plan, and the owner needs to make a decision.
▲ Source: British Road and Bridge Design Manual TD 19/06.
Classical case analysis of road safety evaluation
Case 1: The fork at the corner blocks the line of sight, which is easy to cause accidents.
As shown in the figure below, when approaching the fork, the left guardrail and the road alignment are curved, which may cause the driver not to see the front fork. A large number of brake marks on the road also prove that there are indeed many drivers who suddenly brake at the last minute and change their driving routes.
▲ Figure: The fork road is at the corner, and the driver's line of sight is easily blocked. (Source: Google Street View)
At the same time, there are also some problems in the guiding signs, such as inconsistent information in the sign sequence and new guiding information before bifurcation. In this regard, the review team should summarize the problems, form a report, and explain it to the design unit and the owner. However, it should be noted that the safety review report should briefly explain the types of car accidents that may be caused and give practical improvement plans.
Case 2: The vehicle hit a road sign on the ground, causing serious casualties to passengers.
The fork road in expressway is a high-risk area for vehicle collisions. The following picture is a case: a vehicle hit a guide sign at a fork in the road, causing the driver to die and the passenger to be seriously injured. The street sign structure is made of 100mm*200mm two groups of rectangular steel, which is not easy to deform or collapse when it is hit, and will cause serious injuries to the occupants in the car.
Assuming that the inspection team finds problems in the construction drawing and points out the problems and risks in the inspection report in time, it can give the following three suggestions: First, cancel the road signs. Because the front gantry has relevant warning signs, there is no need to remind them repeatedly; Second, keep the road signs, and adopt circular steel pipes (or the same level) with a diameter of less than 89mm and a thickness of less than 3.2mm, and the spacing between two structural columns is not less than 750mm, or adopt passive and safe energy-absorbing structures; Third, anti-collision pads can be installed, but the price of anti-collision pads is higher. In this case, the best cost-effective method is to use the grass clearing area and cancel the street sign.
▲ Figure: The vehicle hit the road sign at the fork in the road. (Source: Ming Pao)
Case 3: Road visibility is very important for drivers.
This crossing is very dangerous. It is difficult for the driver on the lane to judge that the road ahead is a main road, and the speed on this main road is100 km/h. It can be seen from the debris scattered on the road that the accident caused by the driver's misjudgment has occurred.
▲ Figure: Crossroads that seriously interfere with the driver's sight.
At such an intersection, setting up a diversion island can effectively make the driver of the branch aware of the intersection and force the vehicle to slow down (see the figure below), but pay attention to the visibility of the diversion island at night, and the driver must clearly see the existence of the diversion island.