Nonrecurrent congestion on urban roads may cause overflow, possibly leading to gridlock at intersections. Signal control is one of the most important measures to prevent such phenomena. For nonrecurrent congestion wit...
详细信息
Nonrecurrent congestion on urban roads may cause overflow, possibly leading to gridlock at intersections. Signal control is one of the most important measures to prevent such phenomena. For nonrecurrent congestion with uncertain bottleneck capacity, however, existing signal control methods have mainly adopted the strategy of cutting off the green signal of the overflow movement while the release priority of green time has not been considered. Consequently, the green time allocated to overflow movements is too long, aggravating overflow and congestion. Therefore, a signal control method is proposed to prevent overflow caused by uncertain bottleneck capacity. The proposed method extends existing real-time adaptive signal control to explicitly consider the risk of queue spillover. When an overflow risk is detected, the green times of overflow movements will be reassigned using fuzzy control to determine the release priority depending on the queue length and red time. Numerical studies were conducted for two scenarios with different downstream bottleneck capacities. The results demonstrate that the proposed method not only outperforms existing methods in respect of intersection efficiency but also reduces the risk of overflow. The proposed method achieves a 27.7% to 33.8% reduction in the maximum queue length of overflow movements compared with a traditional adaptive signal control method and a 10.9% to 11.0% decrease compared with a modified signal control method with a cutting-off strategy. The sensitivity analysis indicates that the average delay resulting from the proposed method is 51.1% and 18.0% less than the delays resulting from the traditional and modified methods, respectively.
Various signal control methods assumed that the bottleneck capacity and traffic volume are known. However, both may be unknown in nonrecurrent congestion cases, such as traffic accidents. In this study, a signal contr...
详细信息
Various signal control methods assumed that the bottleneck capacity and traffic volume are known. However, both may be unknown in nonrecurrent congestion cases, such as traffic accidents. In this study, a signal control optimisation method is developed for overflow prevention considering unknown traffic volume and bottleneck dropped capacity. The proposed method predicts remaining space at the junction exits and arrival-departure curves using partial connected vehicle data. Subsequently, the signal control is reallocated using the model predictive control technique. The results of case study show that the model is valid to prevent overflow when the connected vehicle penetration rate exceeds 10%. The average delay of the proposed method is reduced by 48.56% and 24.49% compared with those of the adaptive signal control method considering the queue length of only the approach lanes and that considering the queue lengths of both the approach and exit lanes but without prediction, respectively.
The paper describes the implementation of a 380 MHz, 13 bit, direct digital synthesizer/mixer IC in 0.25 mu m CMOS technology. The circuit employs an innovative architecture which divides the pi/4 rotation operation r...
详细信息
The paper describes the implementation of a 380 MHz, 13 bit, direct digital synthesizer/mixer IC in 0.25 mu m CMOS technology. The circuit employs an innovative architecture which divides the pi/4 rotation operation required in the quadrature synthesizer/mixers, in three rotations. The first two rotations are implemented by using a CORDIC datapath completely realized in carry-save arithmetic. The directions of the CORDIC rotations are computed in parallel by using a little lookup table, for the first rotation, and a multiply by constant and addition circuit for the second rotation. The final (third) rotation is multiplier-based, in order to reduce the circuit latency and increase the circuit performances. The CORDIC datapath is implemented with a novel approach both at the algorithmic level and at the transistor level. At the algorithmic level the combined employ of sign-extension prevention, overflow prevention and a novel rounding scheme are presented. At the transistor level a design style that jointly uses full-CMOS and DPL to improve the circuit latency is described. The overall circuit performances are very interesting. The synthesizer/mixer IC, realized in a 0.25 mu m CMOS technology, has an area occupation of 0.22 mm(2) and dissipates 152 mW at 380 MHz with a supply voltage of 2.5 V.
The effect of roundoff noise in a digital controller is analysed for a sampled-data system in which the digital controller is implemented in a state-space realisation. A new measure, called averaged roundoff noise gai...
详细信息
The effect of roundoff noise in a digital controller is analysed for a sampled-data system in which the digital controller is implemented in a state-space realisation. A new measure, called averaged roundoff noise gain, is derived. Unlike the traditionally used measure, where the analysis is performed based on an equivalent digital control system, this newly defined averaged roundoff noise gain allows one to take consideration of the inter-sample behaviour. It is shown that this measure is a function of the state-space realisation. Noting the fact that the state-space realisations of a digital controller are not unique, the problem of optimum controller structure is to identify those realisations that minimise the averaged roundoff noise gain subject to the I-2-scaling constraint which is for preventing the signals in the controller from overflow. An analytical solution to the problem is presented and a design example is given. Both theoretical analysis and simulation results show that the optimum controller realisations obtained with the proposed approach are superior to those obtained with the traditional analysis based on a digital control system.
暂无评论