Fund project: "Ninth Five-Year" national key scientific and technological research project (96-412-02-01).
2 Basic test Ranging station ranging error Scattering ranging error / H1 v Because GPS data acquisition equipment has the characteristics that the ranging error of two rover stations does not increase with distance, the speed of the rover station is based on two consecutive The secondary positioning is obtained by dividing the distance difference by the time difference. At this time, the absolute error of the rover speed is less than 0.02m / s. If the rover moves within the speed range of 20 ~ 80km / h, the relative error of the rover speed is 0.09% 0.36%; such data accuracy can fully satisfy the vehicle Requirements for car following model research.
3 Application test In order to further understand whether the test vehicle equipped with high-precision GPS is suitable for real-time collection of vehicle following behavior data under actual road traffic conditions, a test was conducted on the highway test field of the Ministry of Communications on June 1, 2001. During the test, the weather was sunny and the temperature was relatively high; the test route was a loop of about 8km, including straight segments and curved segments of different radii; the test model was Cherokee in front and Santana in the back; the test drivers were all young men with a medium driving level Driver; the test instrument is a set of NOVATEL-RT-2 dual frequency receiver (one base station, two rover stations). During the test, the GPS base station was installed on a high ground in the middle of the test site, about 3km away from the test section. There is a high-speed loop between the base station and the rover, and the rover cannot be directly seen. The communication quality of the digital radio between the base station and the rover is good. It can be seen that there are 8 GPS satellites and the signal quality is good. The data output frequency is 5 Hz .The layout of GPS rover and test vehicle is as shown in 丨.
The test was carried out for lh. Through the test, the real-time speed and position information of the bicycle in front of and behind the car in the following state were obtained. The data output format of the two GPS rover stations must be the same when the test is conducted, that is, * GGA * and * VTG * mixed formats. Only in this way can the time synchronization of the two rover stations be guaranteed and real-time speed information can be obtained.
The data obtained directly from the GPS receiver is not suitable for follow-up analysis immediately. After differential and post-processing, the test data is suitable for follow-up analysis on the basis of correcting bit errors and improving the accuracy to mm. Using the GRAFNAV / NET difference and post-processing software of NOVATEL Company to carry out the difference and post-processing on the test data, a total of 9 450 pairs of following status data were obtained. Some data and formats are shown in Table 2.
Table 2 Data format of following behavior after differential and post-processing Front vehicle rear vehicle latitude / (') longitude / r latitude / longitude / GPS rover antenna spacing Rear vehicle front vehicle E. Distance from GPS antenna center to vehicle front end * Head distance The test data can be used to obtain the change trend of front and rear vehicle speed in time series, as shown in Figure 丨 2. It can be seen from the figure: ①The speed trajectory of the rear car (solid line part) basically changes along the speed trajectory of the front car (dashed line part), indicating that the influence of the speed of the front car on the rear car exists. ② Most acceleration and deceleration points show that there is a lag between the speed change of the rear car and the front car.
1 Schematic diagram of the layout of the base station test vehicle. The general expression of the classic following model is as follows: +3 ") is the acceleration of the following vehicle * + r; tu + r) is the speed of the following vehicle * + r; u),, +1) is the speed of the front and rear vehicles at the moment; x * () ,:> (: +1 (the position of the front and rear vehicles at the moment of f; a. Is the sensitivity; w, / is a constant; r is the time interval.
In order to get a specific expression suitable for the car following model under the actual road traffic conditions in China, it must have +, 0 + 7), Table 3 to study the data (part) and the format of the car following model to verify the availability of data, use These experimental data performed regression analysis on the classic car following model. In the analysis, set the time interval r = ls, then the sensitivity is ". = 1. The analysis result is m = -0.4, /=0.9, and the correlation coefficient is 0.31. Since the data used in the regression analysis includes the three following types of stable following state, acceleration state, and deceleration state in the entire following behavior State, because it is experimental data, the data is not screened, and a regression analysis is carried out separately for a follow-up state, resulting in a low correlation coefficient of regression analysis, but the final regression results m and / are similarly studied at home and abroad The result is within the value range (as shown in Table 4). Regression analysis shows that the time-series measured data of rack driver behavior and vehicle operating characteristics in the following state using the GPS-based real-time dynamic vehicle following data collection method can be used to study the following model.
Table 4 Value range of similar research results at home and abroad Source method Micro (1972) (non-brake deceleration, brake deceleration, acceleration) Micro Aron (1988) (deceleration, stable following, acceleration) micro (1933) (deceleration, acceleration) micro 4 Conclusion Through analysis and experiment, it is found that the vehicle-mounted high-precision GPS can record the speed and position information of the vehicle on the actual road and traffic flow, and the accuracy is high; the small size and high portability avoid road conditions to the greatest extent. The impact of the device and the device on the driver ’s driving behavior enhances the “authenticity†of the data; post-processing of the data is more convenient, and regression analysis shows that the data has better usability. Using the GPS-based real-time dynamic vehicle following data collection method can better solve the problem of collecting time series measured data of driver behavior and vehicle operating characteristics under the following state, and is a vehicle following model that truly reflects the characteristics of road traffic conditions in China Of research provides solid data support.
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