1. The Bus Priority Signal System (PTPS): Why Drivers Do Not Operate the Signals
The system that gives priority to buses is called PTPS (Priority Traffic Signal System). As a bus approaches an intersection, a light beacon installed on the road ahead receives near-infrared signals from a dedicated device on the bus, detecting its approach. Then, for the signal in the direction of travel, the system shortens the red time or lengthens the green time [1]. The important point here is that the driver does not press any button. The dedicated machine on the bus and the light beacon on the road communicate with each other, so the signal control happens automatically [2]. So, how is this communication carried out?
2. How a Bus Announces Itself to the Road Beacon with Near-Infrared Light
The dedicated device on the bus emits near-infrared light. When the light beacon on the road receives it, the traffic signal system learns that a bus is approaching [2]. Near-infrared light is invisible to the human eye. While TV remote controls also use infrared, they send a one-way signal. In the case of PTPS, it is said that the ground equipment and the bus device communicate mutually [2]. However, the remote control example is just a comparison to help imagine "sending a signal with invisible light." Once the bus's location is known, what does the signal change?
3. How Signals Extend Green Lights and Shorten Red Lights for Buses
There are two things the signal does: it extends the green light and shortens the red light [1]. If it works well, the bus can pass through the intersection without stopping. The National Police Agency explains the purpose of this system in its Police White Paper. It aims to make the signal green preferentially in the direction of travel so that buses stop as little as possible. This allows more people to be transported at once, improving the punctuality and convenience of buses, which often carry many young children and elderly passengers [3]. In towns without trains, buses are essential for commuting to school or hospitals. The goal is not just to make buses faster, but to reduce the waiting time for everyone who rides them. So, why not just keep the light green whenever a bus comes?
4. Why Traffic Lights Are Not Always Green for Buses
PTPS is not a system that always lets buses through on a green light. It is a mechanism that controls signals according to traffic conditions [2]. Thinking about the reasons generally: there are cars and pedestrians waiting on the crossing roads too. If the green light is extended only for the bus, those people would be kept waiting for a long time. It is necessary to look at the situation and choose carefully so that neither side gains an unfair advantage. In a newer system called Advanced PTPS, it is said that bus detection is done twice, allowing for more flexible adjustment of signal times than before [8]. There are other constraints as well. Compatible traffic signals are required, and the effect is greater in places with heavy traffic. Installing the equipment is difficult without stopping traffic, and budgets are limited [2]. So, how much faster did things actually get?
5. How Much Travel Time PTPS Saved in Chiba, Fujisawa, and Matsue
In Chiba City, on the 2.0 km (about 1.2 miles) route from JR Inage Station to Anagawa Crossroad, introducing PTPS reduced travel time by about 20%. The percentage of buses arriving with less than one minute of delay increased from about 60% before introduction to about 80% [1]. You can read this as about 6 out of 10 buses becoming about 8 out of 10. In the Fujisawa district of Kanagawa Prefecture, on a prefectural road improvement section, travel time was reduced by 5 minutes 22 seconds in the uphill direction and 2 minutes 30 seconds in the downhill direction [5]. Since 5 minutes 22 seconds is 322 seconds and 2 minutes 30 seconds is 150 seconds, the reduction in the uphill direction is about 2.1 times that of the downhill direction. In Matsue City, Shimane Prefecture, the bus punctuality rate rose from 23% to 63%. Since 63 divided by 23 is about 2.7, this is an increase of about 2.7 times. However, the method for calculating the punctuality rate is not clear in this source. It is safer to accept this as a change before and after introduction rather than assuming it is strictly "the percentage of buses with little delay" [6]. Because the three locations and survey methods differ, you cannot simply line up the numbers to rank them. Still, all three regions reported improved indicators after introduction. How far and when has this system spread?
6. How PTPS Spread Across Japan and Is Used for Ambulances
According to the Police White Paper, the number of prefectures that had established PTPS expanded from 27 at the end of fiscal year 2002 to 40 at the end of fiscal year 2013 [3][4]. This calculation shows an increase of 13 prefectures over 11 years. Originally, it spread to support the punctuality of route buses, but there is another system called FAST (Field Ambulance Support System), which is also introduced as controlling signals to give priority to emergency vehicles like ambulances [7]. Alongside the system supporting bus punctuality, there is also a signal system used in life-threatening situations.
7. Try It Yourself: Observe Traffic Signals at a Bus Intersection
Try observing traffic lights from the sidewalk at an intersection where buses frequently pass. Do not step onto the road. Use the second hand of a watch to compare the length of the green light when a bus comes versus when it does not, several times, and record any differences you notice. However, from the outside, you cannot know if PTPS is installed at that intersection or what the signal used to make its decision. Even if you see a difference, it might be due to other conditions like traffic volume, so you cannot say PTPS worked. It is not a mistake if you see no change on some days. To read the original sources, the National Police Agency's Police White Papers (2003 and 2014 editions) are primary documents. The Kanagawa Prefectural Police page on congestion countermeasures lists examples of improved sections. The application to ambulances (FAST) is also a good next question to explore.