Communications: electrical – External condition vehicle-mounted indicator or alarm – Highway information
Reexamination Certificate
1999-02-05
2001-11-20
Tong, Nina (Department: 2632)
Communications: electrical
External condition vehicle-mounted indicator or alarm
Highway information
C340S907000, C340S911000, C340S917000, C340S918000, C340S919000, C340S934000
Reexamination Certificate
active
06320515
ABSTRACT:
BACKGROUND OF THE INVENTION
Short Information about the Invention as System Controlled Access (SCA)
The system controlled access is designed by several coordinated steps. Actions are taken at the road net on different distances from the given access point. Far upstream, traffic control actions are introduced, that e g might limit average flows in to SCA, i e for an average time period, some minutes or less, a controlled amount of cars will arrive. During the travel towards the motorway access, those cars however might pack together to various dense “car-packets”, which implies that during short time periods of less than a minute, large differences from the average flow might arise. Those differences have to be considered at e g closer positioned accesses, not allowing many cars at the access at the same time as there are a package of dense traffic on the motorway. Otherwise all the cars haven't space enough for weaving, and the traffic collapses resulting in queue build up and high risk for accidents.
By regulating the access traffic in relation to the motorway traffic, the traffic density is smoothed for the downstream motorway link. However there are many factors working in the opposite direction, why traffic successively will distribute according to statistical distributions. Thus one might measure a certain traffic distribution at one spot on the motorway, which is different from the traffic distribution some kms further downstream. Differences in detailed traffic distribution arise also if there are no access or exits in between. That means that one often has to consider newly and closely arisen variations, when striving for an effective traffic control.
So there is also a need for a final control at the waving area to achieve a safe and efficient traffic access. An important part of the invention considers that last phase of the access control.
The invention can be regarded as a system of actions on four different levels. The first level is “Access control along a motorway” and is based on traffic management of a road-network, considering various access roads, as other motorways, connections to city street-network etc.
The second level is “preparatory weaving”, which is performed on the motorway upstream exits and access-roads.
The third level is “preparatory actions”, which are performed just before the “ramp”.
The fourth level is the “local level” at the position of the ramp.
The four levels can work together and combine to an efficient and safe access traffic. But compared to to-day situation, every level by itself can be implemented resulting in improved access control. The invention concerns a system-based improvement of access traffic control, where the different levels can be implemented one by itself, or in combinations to various extent, or successively at different occasions, possibly as steps in a planned expansion, or within a given short time period to obtain a more direct cooperation of the applied levels.
TRADITIONAL ACCESS CONTROLS
The most used on-flow “control” is free weaving of traffic from the access road into the motorway, but with certain rules giving the motorway traffic priority, i e the cars from the access-road should adapt and weave into the gaps between the cars of the motorway. When the traffic flow on the motorway is close to its maximum, there aren't enough safety margins to put cars into the small existing gaps. If a car anyhow turns into such a gap, the driver wants to start braking to increase the distance to the car in front of him.
The car behind, then has to brake even harder, partly because his gap shouldn't decrease and partly because the distance gap was too small already from start. Simply said, the braking need has doubled. Then if more cars are weaving into gaps between the following cars already braking to keep their safety distances, then the result soon turns into a traffic collapse with queue build up and large risk for accidents. Similar collapses occur also when the motorway traffic is less dense, but the access traffic flow is higher, giving the total flow above the access weaving capacity.
TRADITIONAL “RAMP-METERING”
The concept of ramp-metering is often described as a way to limit the access flow to the ramp, not allowing more vehicles to enter than what gap space there are on the motorway. When there are periods with lower traffic flow on the motorway, more cars can be allowed to access, and if it is very dense traffic on the motorway, no cars are allowed and so on. The access is regulated by traffic signals. If there are too many cars in a row on the access road, they will be lined up in queue, and one car a time is allowed, when the traffic light signal turns green for some second.
The problem with ramp-metering is that it is not operating that well adapted to the traffic. Certainly the motorway is equipped with sensors, positioned just upstream the ramp (e g a couple of hundred meters) and thus measure the traffic at that position. But there are two problems, when one wants to utilize those measurement values for controlling the access traffic. One problem is usually too long measurement periods e g a minute. That implies that before the measurement period has ended, the first cars have had time to run for almost a minute, meaning that they have passed a distance of 1800 m (L=v*t) at a speed of 110 km/h. Most of the cars thus have already passed the weaving area before even the measurement period has ended. That measurement intended for giving knowledge about how many cars, that are on their way to the weaving area, for the intended succeeding control of the ramp-meter according to just that traffic. The other problem is that the light signal has to be positioned far upstream on the access road, giving the stopped cars a long enough distance of acceleration to reach the speed (110 km/h) of the motorway traffic. They should have the same speed as the motorway cars to be able to weave into the motorway traffic in a smooth safe way. It means that controlling the ramp-meter according to the measured values, it will take further some 20 to 30 seconds (t=v/a), before the access road cars have reached the weaving zone, i e the traffic, that now is on the motorway, is quite another traffic than has been measured, and the measured traffic has already passed.
Thus the measurement should be carried out at least the distance L=v*t=v*v/a==v
2
/a upstream of the weaving area.
It seems that those traffic engineers that use ramp-meters, haven't understood the problem. Accordingly there are some secret magic about those algorithms and methods used on the measured values to optimize in what time period the cars should be allowed to pass the metering signal. Generally the methods also use more than one measurement period value, to reach their results, which means that they are trying even harder to adapt the access traffic to that traffic on the motorway that have passed since still longer time ago.
OTHER KNOWN TECHNIQUE
In the Swedish patents 9203474-3 and 9501919-6 methods are described for predicting traffic and detecting incidents and traffic collapses. Those methods are generally applicable for traffic management on the whole road network, and are also useful at access control. Those methods are postulated known, and when prediction and queue-detection etc are mentioned in connection with the present invention, those methods are good examples of how to perform such matters.
Access control by ramp-metering has been used for a long time period, not least in U.S. The methods have their deficiencies and is generally not really operating in that way as it is described. That was described in the section Traditional “ramp-metering”. Here we shall discuss some chosen known examples on methods, which have been suggested for use in connection with access roads and lane changes.
There are ideas on building “car-trains” or platoons of cars on motorways for increasing the capacity very much. The cars are going to be automatically controlled, driven very close to each other (e g a
Connolly Bove & Lodge & Hutz LLP
Tong Nina
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