Design of Deceleration Lane in Interchange
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â–¡æ–‡/é‡‘æ ‘æ³•ä¾¯æ¸…æŽæµ·æ³¢ The road traffic industry has become a pioneer in economic development and the people's prosperity in the reform and opening up. With the deepening of reform, the road traffic industry has also developed by leaps and bounds, especially the rise of highways and urban expressways. With the construction, the country and the people are all fascinated by the road traffic industry, and the construction and management of the road has already mentioned a fairly high agenda. Since the 1980s, with the development of China's high-grade highways, road interchanges have also achieved breakthroughs from scratch. In the current 37-90), there are also relatively perfect regulations for the design of interchanges, but the design methods and the application of theories and indicators will vary from person to person.
There are two main methods for designing a deceleration lane for a single lane deceleration lane: the general design method and the North American design method.
It has been used by many designers for many years. The author describes the design method of the deceleration lane with a design example.
Example 1: Main line. Calculate the driving speed: 120km/h, see the cross-section arrangement.
=11.625m position) is the starting point, and the straight line is outwardly biased at a gradual rate of 1/25. When the ramp lane is outwardly offset from the outer lane of the main line by one lane width (ie 1.5+0.75 from the main line design centerline) +3.75x3+0.5+3.5/2=15.75m position) When the position (ie 8 points) is the end point of the transition section, that is, the starting point of the deceleration lane, the length of the transition section is 103m, which meets the requirements of the specification.
After the end of the transition section of 2006, the gradual transition rate of 1/25 will continue to be outward. At the end of the C-speed deceleration lane, the design of the SC-segment deceleration lane adopts the form of linear acceleration and curve. The length of the deceleration lane is 145m. Meet the requirements of the specification.
In order to ensure that the vehicle leaving the main line can maintain the main line within a certain driving distance. However, the linear shape of the deceleration lane does not have to be consistent with the main line, mainly due to the selection of the designer. In general, the use of the mitigation curve is more common, no matter which linear shape is adopted, as long as the value used can meet the requirements of the length of the deceleration lane.
In addition, it should be noted that after the flat longitudinal line design is completed, the radius of curvature of the split point and the length of the deceleration lane should be checked. When the deceleration lane is downhill, the length should be adjusted by the correction factor. The value of the correction factor is shown in Table 1. Table 1 Downhill Deceleration Lane Correction Coefficient Main Line Average Slope % Downhill Deceleration Lane Correction Coefficient) The length of the gradual section is generally longer than the deceleration lane, and the position where the main line turning vehicle begins to deviate is not obvious;) When the alignment is not known, where is the starting point of the deceleration lane? , need to calculate;) When the main line is a curve, the exit gradation rate at the starting point of the deceleration lane is not easy to control.
In view of the above defects in the general design law, China introduced another design method for deceleration lanes from North American countries in the early 1990s, namely the North American Design Law. The difference from the general design method is the starting point of the rifling alignment. The North American design method starts directly from the starting point of the deceleration lane, that is, point B in the figure (the position of the lane width is offset from the main line), and then is offset by a straight line and a large radius curve. Point A is the starting point of the gradient segment, which can be selected according to the specifications of the length of the gradient segment.
The North American design method overcomes the shortcomings of the general design method: the length of the gradual section can be controlled freely, and the exit position of the main line is more obvious. When the line is fixed, the starting position of the deceleration lane can be determined, and the exit gradation rate control is also easier.
Two-lane deceleration lane design When the ramp is a one-way two-lane, the deceleration lane is divided into two forms according to whether it is necessary to set an auxiliary lane.
The design of the two-lane deceleration lane with auxiliary lanes is set. When the number of main lanes before and after the diversion point of the main line and the ramp is constant, according to the principle of lane number balance, the main line should be set with an auxiliary lane of a fixed length before the branching point.
See, at point E of the normal road section, the main line is a 3-lane section, and the main line of the diversion point/point is still 3 lanes. The auxiliary lane of the FG section needs to be set to ensure the balance of the number of lanes.
The starting point of the deceleration lane alignment is G point (ie, the lane boundary line between the outermost lane of the main line and the auxiliary lane, and the distance from the main line design line is 1.5+0.75+3.75x3=13.5m), with a straight line of 1/22 gradient rate Outside the deviation, the length of the split point/point is 225m for the two-lane deceleration lane, which meets the requirements of the specification. At the same time, it is also necessary to check the length of the inner single lane deceleration lane when the inner lane is offset from the outer lane of the main line by a lane width (1.5+0.75+3.75x4=17.25m from the main line design center line, ie H point). It is 155m, which meets the requirements of the length of the single lane deceleration lane under the corresponding driving speed. The hard line of the main line is gradually changed to a width corresponding to the hard shoulder of the ramp in the range of the ramp at a gradient of 1:30, ending the design of the deceleration lane.
Two-lane deceleration lane design without auxiliary lane This form of two-lane deceleration lane extends outward at a certain gradual rate after the diversion point of the main line and the ramp, and the lane boundary line (/C point) of the two lanes outside the main line Until the outer lane of the ramp is offset from the outermost lane of the main line by a lane width position (point L) as the starting point of the two-lane deceleration lane, the inner lane of the ramp is offset by one lane width from the outermost lane of the main line. The position (point M) is the starting point of the inner deceleration lane, and the M point of the nose is still the end of the lane. The distance between the M and W points is close to the specified length of the single lane shift lane. The distance between the L and W points should meet the specifications for the length of the two lanes. The main line hard shoulder is gradually changed to the width of the ramp shoulder with a gradient of 1:30 in the range of the ramp. For example, between W and 0 is the hard shoulder gradient of the ramp.
The design method of this type of deceleration lane is basically the same except that the starting point position of the line is different from the general design method of the single lane deceleration lane. The other design methods are basically the same.
Indicator control points near the deceleration lane diversion point) Length of the transition section. The direct deceleration lane adopts the general design method, and the gradient rate is not too large (usually not more than 1/20), which can meet the requirements of the specification for the length of the transition section. The North American design rule is more flexible, and the length of the gradient section can be adjusted to a large extent, which is easy to meet the specification requirements.
Deceleration lane length. A deceleration lane of sufficient length should be set during the design process. The problem in the current design is that most designers do not consider the correction of the length of the deceleration lane when the main line is more than 2% downhill. This will have certain safety hazards in the highways with large vertical slopes. . ) The radius of curvature of the split point. Care should be taken not to confuse the radius of curvature with the radius of the circle curve. Any curve that can be expressed by a mathematical formula (including a straight line) has a certain radius of curvature at a certain point. The radius of curvature of the line is infinite. The easing curve is a curve that changes from a radius of curvature value of the endpoint to a radius of curvature of the end point.
(4) The mitigation curve parameters of the ramp diversion point. In addition to the parameters, the mitigation curve should meet the requirements of the specification for the parameter values. It should also be noted that the length of the mitigation curve after the shunt point should not be too short, otherwise it is difficult to meet the demand for the ultra-high transition of the ramp.
The collection and distribution lanes and the deceleration lane design distribution lanes are generally arranged between two inter-connected interchanges with close spacing, or in a typical crotch-type interchange. Its function is to eliminate the interweaving on the main line, so that the traffic flowing into the main line and the traffic flowing out of the main line do not cause excessive interference to the main line, and improve the traffic capacity and driving safety of the interchange.
The distribution lanes and the main line straight-through vehicles within the interchange may be separated by physical separation facilities or markings.
The expressway interchange interchange lane design is in the expressway interchange. Because the speed is generally high, the distribution lanes are generally separated from the main line straight-through vehicles for physical separation. A set of distributed lanes for setting a 2m wide separation belt.
The vehicle that wants to enter the ring road from the main line first goes through the deceleration transition line to the deceleration lane into the â–¡, decelerates to the ramp speed in the deceleration lane, and then enters the distribution lane interleaving area to enter the ring ramp Z1 to complete the left turn function.
The vehicle should complete the lateral offset process from the main lane to the collection lane in the deceleration transition section. The lateral movement distance is longer and the vehicle speed is higher at this time. Therefore, the length of the deceleration transition section of the collection lane should not be taken according to the length of the general deceleration lane transition section. Value, but the length of the gradient segment should be calculated according to the width gradient of 1/20-1/30. This length should not be less than the specification's requirement for the length of the transition segment.
The length of the deceleration lane after the end of the transition section shall not be less than the length specified in the specification.
Urban road interchange interchange design is designed in the city interchange. In order to meet the normal traffic requirements of non-motor vehicle lanes and pedestrians, the distribution lanes are mostly arranged on the bridges, and the calculation speed is generally lower than that of the highways. Therefore, the distribution lanes and the main line can be between the vehicles. Separated by lines.
That is, the form of a distributed lane that sets a 0.5m wide marked line area.
The design method of the 0B-B section of this technology V to use the traffic marking to separate the main lane and the distribution lane is basically the same as the design method of setting the physical separation. Refer to the design method of the physical separation of the collection lane.
The line design of the interchange is a complicated task. According to the natural conditions of the site, traffic, roads, drainage, etc., the line shape is ever-changing, and different designers have different design habits, which makes the current intersection line design method difficult to unify, especially the details. The design is also very different between different regions and even different design institutes. The author's purpose in writing this article is to discuss the best design method with the majority of designers, in the hope of unification of the intersection line design method.