Coordinating on-ramp queue control with adjacent local signal controller: an algorithm to assist ramp metering application
This paper describes a queue control algorithm which is able to coordinate its operation with that of an adjacent local signal control so that its efficiency is improved. A microscopic simulation model (AIMSUN) was used to test the operation of the new queue control algorithm and compare its performance with that of the standard queue control. The assessment has shown the new algorithm to be a significant improvement in reducing the variation of the release rate and the frequency of exceeding the storage capacity whilst the efficiency of utilising ramp space increased. Also, the new algorithm was found to be less sensitive to changes in ramp demand and some parameter settings originally found critical to the operation of standard queue control. For the covering abstract see ITRD E134653.
The benefit of video detection for onramp queue control and ALINEA ramp metering strategy
Ramp metering (or on-ramp traffic restriction) aims to optimize traffic conditions in the vicinity of a motorway merging section. However, to prevent excessive on-ramp queues from disrupting adjacent local road network, they have to be managed properly. Traditionally, occupancy measurements from on-ramp induction loops were used to activate queue-over-ride operation when certain threshold is exceeded. One of the aims of the European project RHYTHM was to assess the benefit of utilizing video detection technology for on-ramp queue management of ramp metering. A new queue control algorithm integrated into ALINEA strategy was developed to utilize the on-ramp queue length information provided by video detection. A microscopic simulation model (FLOWSIM) was used for evaluating the new ramp metering prototype. The test site was a model of the Mnchen-Messe Riem junction at the A94 near Munich, Germany which is the RHYTHM real test site. Three levels of ramp demands were used (500, 600 and 700veh/h) and several simulation runs with different random seeds were undertaken to ensure the reliability of results. The evaluation used a number of assessment measures including total vehicle travel time and the time of on-ramp queue valuation to maximum ramp length. The traffic condition without metering was considered as a reference base and the new prototype was compared with two other metering situations: (i) ALINEA without any on-ramp queue control. (ii) ALINEA with simple queue control using induction loops. the impact of ramp metering was reduced significantly when ramp queues were considered. However, without on-ramp queue control, the time of queue valuation to maximum storage space was very large (more than 50% of the time) so that the benefit of ramp metering in such case is likely to be void. The larger the ramp demands the lower the impact of ramp metering with queue control as on-ramp queues build up quickly activating queue-over-ride more often. The total vehicle travel time was reduced by 24% (positive impact) when ramp demand was 500veh/h while it increased of 2% (negative impact) when ramp demand was 700veh/h. The assessment has also shown that video detection and the new on-ramp queue management algorithm has contributed to better results compared to traditional loop-occupancy approach. It helped to reduce the time of queue valuation to maximum storage space and to improve the impact of ramp metering when ramp demand was appropriate. For the covering abstract please see ITRD E135207.
Ocean thermal energy conversion: The promise of a clean future
Due to the world's heavy dependence on fossil fuels for electricity, pollution and global warming is on the rise. However, numerous countries are still relying on diesel generators as their main source of energy. There is a lack of practical alternative energy source that can meet the global energy demand without posing any threat to the natural environment. Ocean Thermal Energy Conversion (OTEC) is a concept that has the potential to address this growing issue. It is basically a mechanism that exploits the temperature difference between warm surface seawater and cold deep ocean water, to produce electricity. Although OTEC has a low energy density, the thermal energy in the ocean is vastly abundant. OTEC development has been dormant for a long time since it was first proposed in 1881. However, it has now regained recognition worldwide as a realistic solution to our world energy issue. Instead of having a great potential for power generation, it also carries the ability to produce high value products from the large volume of Deep Sea Water (DSW) that can be released as byproducts of OTEC plant operation. These products can hold a very profitable place in industries such as pharmaceutical, food, cosmetics and mineral water production. Further research on ocean current and DSW properties can someday lead to the commercial used of OTEC. This paper is a review of the basic concept, present status and future prospects of OTEC around the world.