Vehicle stationing – optimization of passage of PT vehicles through intersections

After the passengers get on, public transportation vehicles often leave stations situated in front of intersections and immediately stop at the traffic lights where they wait for the green light. This time can be used for more passengers to board the vehicle providing that the vehicle spends it at the stop. Moreover, setting the vehicle in motion and stopping it almost immediately leads to higher consumption and wear (break system components, components prone to dynamics) and also to significant production of exhaust gas. „Vehicle stationing“ is a way to limit these situations. This principle is a part of the modern vehicle preference system.

Various versions of  public transportation vehicle preference systems are commonly used in many cities – with uni- or bidirectional communication between a public transportation vehicle and an intersection controller. In the case of the more frequent unidirectional communication of a vehicle with an intersection controller, the controller is only informed about the arrival of the vehicle. Based on the current internal state the controller decides whether and what kind of preference will be assigned to the vehicle. In the vehicle, only the delivery of the request to the controller is checked but not the result of its decision. Historically, this communication was realized by using common radio channels and radio data modems. The result of this communication could be either a series of green lights or a change of light on the traffic lights. The driver only found out from the change of the state of the lights.

 Possibilities of using the new technology V2X

Currently, this communication can be solved by using the newly introduced international standards V2X and C2X (communication of a vehicle with its surroundings) on the 5,9 Ghz frequency. It is also a system that was tested in the Czech Republic during the C-ROADS international project of implementing ITS systems in transportation. The technology itself is designed for general communication of a vehicle with its surroundings. All the public transportation vehicles of the Brno Public Transport Authority plc. (DPMB) and the Ostrava Transportation Company plc. (DPO) are equipped with this communication technology.

Although the V2X system is currently used for public transportation preference only in DPMB plc., this technology brings a number of advantages:

• Communication channel standardization – the V2X technology brings the benefit of a clear communication channel definition. In the Czech Republic, a number of different preference types are used. In a system, this „disunity“ causes problems when adding new preference participants – emergency services and regional public transportation whose vehicles also frequent cities. The V2X standard clearly defines communication rules, therefore using this technology removes the dependence on manufacturers of controller and communication unit, and transportation providers. It is up to the „city“ to decide how transportation is to be organized.
• Communication security – radio communication brought new ways of direct communication, but its security depended on using simple single-purpose communication protocols. Communication using the V2X technology introduces asymmetric cryptography and certificates with public and non-public keys (signatures). This communication cannot be misused without knowing them by any subjects to e.g. obtain preference (in the case of the other types it is just an issue of technical means and an appropriate analysis).
• Digital communication – the classic radio communication provided a simple solution, but radio signals are less resistant to interference whatever their frequency. The V2X technology is based on principles similar to Wi-Fi which makes it more reliable.
• Further development – the V2X standard clears way for other functions given by the protocol attributes – e.g. tram collision detection achieved by using vehicle – vehicle communication, direct communication between a vehicle and a stop sign, etc..

What is „vehicle stationing“

The term „stationing“ is not known by the public and it is hard to describe by sing vehicle operation terms. However, its results can be interesting. Its basis consists of intelligent communication between (not only) a public transportation vehicle and an intersection controller – little used bidirectional communication between a public transportation vehicle and an intersection controller (now implemented in Zlín, Jihlava, and Ostrava).

What stationing means:

• The term stationing in public transportation means „passing through an intersection with previously stopping at a stop“. It denotes that a vehicle stops at a stop in front of an intersection (in its „bay“ or at a traffic island, directly at the body itself).
• The stationing principle is based on coordinating the vehicle from the stop in front of an intersection. The vehicle only leaves when it receives a „command“ from the intersection controller. The stationing system is not (or does not have to be) directly connected to public transportation vehicle preference, but it optimizes departures.
• There are two advantages of stationing – it makes passenger boarding more convenient as the vehicle does not leave the stop prematurely, and it prevents double vehicle starts – first towards the traffic light and then when the green light is on. This makes public transportation more attractive to passengers and less harmful to the vehicles and the environment which brings ecological and economical benefits.

How does it work (functions of individual points):

1)      Before arrival (1) to the stop, the vehicle reports to the intersection controller. The stop is situated between the first reporting point and the second reporting point (reporting correction point).

2)      The vehicle gets a command from the controller that it is to remain in the bay (3) until the controller commands otherwise. The driver receives this information on the display of the on-board computer – the „red“ is on. The vehicle remains at the stop, its doors are open, and passengers can board it.

3)      The vehicle receives the information that it can continue on its route (4) as the green light will be on in its direction in x seconds. The vehicle is given a „guaranteed“ green light, and when it comes to the intersection, it passes through freely. The information is delivered to the driver via the on-board computer.

4)      The vehicle informs the controller unit about its departure from the stop, its position on the route (point 2), and its passage through the intersection (point 5). If the vehicle gets delayed at the stop the whole process is repeated until the vehicle utilizes it.

 Stationing system – not only economical benefits

As already stated: If „stationing“ is not utilized it means that from the point of view of driver behavior: after passengers board the vehicle, the doors are closed and the vehicle „sets off“ towards the intersection, i.e. it starts moving and often stops again.

The price of setting a vehicle in motion and achieving a certain speed can be calculated based on the cost of fuel/energy and its consumption. Consumption differs based on the technical state of the vehicle and its weight which is significantly affected by its occupancy. The price of achieving the speed of 30 km/h is not negligible (the prices are from 2018 and were averaged for various categories based on the type of traction). The presented graph shows that a bus has the „most expensive“ start, and vehicles with electric propulsion are more ecological.

Let us have a look at a real life example from a given intersection. Given vehicle types pass through this intersection (coupled trams, T13 trams, K2, Anitra, joint Varia, and KT8). On average setting these types in motion to reach 30 km/t at their full capacity costs – 1,56 CZK.

We chose the Pekařská – Úvoz intersection for the purpose of this example. It is situated in Brno and it is suitable for stationing. During the current traffic limited by COVID-19, there are 538 passages in total during work days and 404 passages in total during non-working days, all this during the time when traffic lights control the traffic.

During the current state, if only 50% of trams use stationing it means:

• 269 passages during work days
• 202 passages during non-working days.

If we calculate all this for the whole 2020, which has 251 work days and 114 non-working days, we can use multiplication to get the costs:

• 251 x 270 x 1,56 = 105 721,- CZK for work days
• 114 x 202 x 1,56 =   35 924,- CZK for non-working days.

When we add up these costs for one given intersection and given vehicle types that really pass through this intersection, the average cost of 140 000 CZK a year for electric energy can be avoided. When statistically considering only 50% of trams, the actual number would be a little lower as not all drivers respect these principles, and trams are not always fully occupied. Further savings are to be found in lower wear of vehicle parts.

 What is needed for the „stationing“ function?

As mentioned above, stationing is often referred to as connected with the public transportation vehicle preference function. This functionality was gradually derived during implementation of preference. The ideal means to implement stationing is using the standardized V2X communication technology that is described above.

The following modifications have to be implemented for the whole preference system to function:

• Addition of V2X communication units to vehicles (sometimes called OBU – On Board Unit).
• Modification of the behavior of on-board computers (transfer of „green“ and „red“ notifications from an intersection controller directly to the screen of an on-board computer).
• Expansion of the RSU communication unit in an intersection controller to provide bidirectional V2X communication with vehicles.
• Modification of SW in an intersection controller to provide communication with RSU units (intersection controllers may not be able to do it).

A controller has to know that a vehicle is located in the monitored zone and work with that information. On the other hand a vehicle has to know where it is located to be able to process these commands, i.e. send a command, receive a command and inform the driver about the departure command.

Conclusion

Even if the described system does not provide public transport preference, it will still make traveling more pleasant and provide energy savings (electricity, diesel, gas). It will make public transportation and mainly buses much cleaner.

Thus the system brings non-economic aspects including:

• Convenient passenger boarding – vehicles can stay at stops longer and passengers can board them conveniently.
• Lower emissions and noise produced by road vehicles – each vehicle start brings increased exhaust gas production, energy consumption, and engine noise.
• Traffic security – each organized departure from an intersection will bring lower probability of accidents, and drivers will not be forced to go at „orange“.

The above calculations show that even with one-time investments in new vehicle and intersection technologies economic benefits are to be expected that will pay for the technological development.

About the company

The Herman company has a lot of experience with the stationing and public transportation preference functionality. One of the first „stationing“ implementations took place in Zlín and then in Jihlava and Ostrava as a part of  common radio operation. During the C-ROADS project, the Herman company successfully implemented the V2X technology and preference of public transportation and ES. A new FW was developed for V2X communication units used for intersection RSU, and communication with intersection controllers (RSU – controller) was modified  as a part of the solution.  The „stationing“ function is in compliance with using the V2X technology.

More about stationing on www.herman.cz.

The passage and consumption examples were provided by DPMB plc.

Text and photo: Ing. Ivo Herman, CSc.