Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Traffic analysis or control of surface vehicle
Reexamination Certificate
2000-07-27
2002-12-17
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Traffic analysis or control of surface vehicle
C701S118000
Reexamination Certificate
active
06496773
ABSTRACT:
THE INVENTION
The invention concerns a method and means for maintaining and using a large capacity at a road network. It includes performing the method during time periods, when there are large traffic volumes and needs for large capacities. The method is focusing on reductions of blockings and risks for blocking of flows on links in a road network. One method step is limiting upstream flow to reduce risks for blocking of a downstrearn link. The method is using several method steps at different levels. Those steps cooperate to make a traffic management possible, which works in real time with traffic network functions.
BACKGROUND
Prior Art
Traffic volumes are large during rush hours, and there are built up queues at the road network in and outside large cities. It is difficult to get space for more roads and those are expensive to build. By using advanced information technology, the present capacity of the road network can be used more efficient and larger traffic volumes can be managed with less additions of new road capacity.
This matter is reflected by the large interest devoted for ITS, Intelligent Transport Systems. within EU, US and Japan and others during the nineteen nineties.
However there are no solutions known yet, why there are large amounts of money put into research in the field, and various ideas are studied.
Traditionally one has tried to solve capacity problems at the road network, by building more roads or taking actions at those points, where the problems appear. If there are long queues on a road upstream of an intersection, one is trying increasing the passability through the intersection for the cars on the said road. This is the traditional way of regarding traffic problems. The problems are narrow sections at the road network. At those points traffic queues are arisen, and then the solution is regarded to be increasing the capacity at those points.
With more knowledge in traffic and the network characteristics of traffic, the traditional “point oriented” way of work seems superficial and providing shortcomings. Resulting “solutions” might create larger problems than the problem considered. An example is given as follows.
It is common that there are queues on the entrance roads of large cities during the morning rush hours. A queue might arise at a narrow section, eg at an on-ramp to the entrance road, and one might increase the passability here, e g by adding an extra lane. The resulting increased flow might come to a stop at a “new” narrow section close downstream, whereby queues are created here instead. The queue at this new position might create larger traffic problems than the queue at the first position.
There are needs for a more system oriented way of work to solve traffic problems at road networks.
Methods described in literature are mainly concerning light signal controls of intersections. Most of the methods are point oriented and concern optimising one intersection for increased capacity. There are also various methods connecting controls of a few intersections along a larger traffic “arterial” to produce a synchronised control of those intersections, a type of “green wave”. The green wave however is a “solution” that is focusing on one of many aspects for a road network, like the corresponding “point oriented” way of work. The negative consequencies for traffic can grew large. It is also common to change methods from e g “green wave” to independent intersection control, depending on the traffic load In those cases a dilemma arises utilising the full intersection capacity. For timeplan controlled intersections there should be a full outflow at green signals from each inlink to the intersection. This can be done if each link contains queues, which supply the whole green periods with passing cars. Queues however are not desired from other points of views. They increase travel times (and drivers' stomach acidity).
There are intersection controls, which to a larger extent adapt the green time length according to the amount of cars that are on the road. By measuring the flow a bit upstream, one knows if there are more cars arriving, and can increase the green time period correspondingly. In this way more green time can be taken from a link, that doesn't need its share, to a link that needs more.
In short, there have been large efforts focused on obtaining increased passability through intersections. That is also a natural consequence of the matter, that a light signal controlled intersection only provides 20-40% of the inlink capacity. Variations in capacity depend on the intersection design, the share of left turnings, safety aspects and the used timeplan policy. The present invention also concerns providing large capacities. In the invention however the network orientation is dominating and system oriented solutions are invented. Those solutions consider the network capacity in a management coordinating way. Also in the present invention the capacity of a single intersection is of interest. But then it is related to other requirements and conditions.
The present invention differs already in applying a different problem view on traffic, compared with the traditional one, described above. The invention includes a new way of considering traffic problems, a new way of managing traffic and a new way of solving traffic problems.
We will start looking on some traffic problems, and we start simply with problems related to intersections, as such matters were discussed above.
The Invention Problem View
Example on traffic problems.
Let us choose a light signal controlled intersection.
A link entering the intersection consists of two lanes, which closest to the intersection have been extended with an extra third lane, for those cars turning to the left. This extra lane has got space for five cars in a row. When the signal is green for cars heading straight, it is red for the left turning cars. When the left-turning lane is full of cars the rest of the left turning cars have to queue up in the ordinary left lane, why there only is left one lane for those heading straight. Then the passability is halved, and the cars that don't get time to pass during the green period, are queueing up in both lanes.
When green for left turnings, those cars in the left-turning lane can pass the intersection. Those cars stopped behind in the queue, cannot pass the queueing cars in front of them and thus cannot utilize the green time for turning left. New cars are let in to the link from the upstream intersection. Those cars add on to the queue. When the light signal turns green again for going straight ahead, the passability once again is reduced, after that the left-tuming lane has been filled. Left-turning cars are blocking the “straight ahead” flow, and “straight-ahead” cars are blocking the left-turning flow. The capacity out from the link is decreasing, and if the capacity and flow in to the link is unchanged, the queue on the link is growing, until the queue is covering the whole link. Then cars from the upstream intersection cannot enter the link, although it is green light for the entrance roads to that intersection. This results in queues of stopped cars on the entrance roads, though the signal is green. Those queues in their turn block those cars on the entrance roads, that are heading for other roads out from the intersection. Thereby the outflows from all three entrance roads can be blocked, and their respective capacity turns to be very low, why the queues on those three links grow very fast and reach their respective upstream intersection, which in its turn is blocked, whereby its three entrance roads will be blocked and so on.
Observe that the blocking effect might give a very large gearing effect concerning the reduction of capacity. Say for instance that the first link (
1
) in the example above, gets its capacity reduced to ⅔. Upstream entrance road (
2
), which includes right-turing cars in to the first link, might get further reduced capacity. If right-turning cars consist of 20% of the flow of link (
2
), and ⅔ can pass into li
Connolly Bove & Lodge & Hutz LLP
Cuchlinski Jr. William A.
Hernandez Olga
Hume Larry J.
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