60 Kangaroo Ground Road North Warrandyte

Driveway Safeworking System

The term "safeworking System" comes from railway practice where sometimes elaborate systems are set up to keep moving trains apart and avoid collisions. On single track sections of railway (one track used alternatively for both directions) there is always a system in place to prevent trains entering that section from both ends at once.

On our driveway, speeds are low and visibility exceeds stopping distance. There is no danger of head-on collisions. Cars entering the driveway at both ends at once could cause a potentially serious situation however. Where there is no room to pass, one car or the other would have to reverse out, possibly for more than 100 metres. Some drivers are not confident to tackle such a move, and even with good drivers, it can be very difficult if a trailor is under tow. We set out to avoid this.

Most car drivers will not be conversant with railway signalling practice, but all will be familiar with traffic lights. The one indication that will be required here that they will not be familiar with: "back out to make way for oncoming traffic" is easily added to the familiar traffic light repertoir. In this case with a flashing red light, and a sign explaining the meaning.

Here, then, is a proposed system.

Starting from the road outside the gate, we have some type of signal for those in the know. The details are not thought up, but the idea is that for aesthetic reasons, it will not be noticable, but for someone who knows what to look for, it is immediatly obvious. This indicator is to indicate "car travelling up the hill", and will enable the driver in the know to wait up on the road. This indicator will have to be obvious at some diatance for cars coming from the bridge. (Cars travelling North from the Warrandyte township. This traffic encounters the front gate on the right.) They will want to veer left and pause at the side of the road. It is inappropriate to block entry to a car that is already stopped in the middle of the road with the right turn indicator flashing.

One could argue for a signal that would be inderstanable to all, but that would have to be so large and unsightly, that the notion is rejected on aesthetic grounds.

Once in the drive, the driver encounters a coloured light signal styled to look like a "Traffic Light" so that the purpose is clear to all car drivers. This is placed on the right side of the drive and about a car length past the small refuge behind the Services Cupboard.

On the post, is a sign which reads "If red light is flashing, reverse to clear drive for uphill traffic".

If the driver encounters the red light flashing, she can reverse into the refuge behind the services cupboard.

During common moves, this light would never show a plain red aspect, but it would be possible to bring a car to a stop at this point.

If the light is green, the car proceeds down the drive.

Near the house, a post is encountered with two signs on it.

The first reads "Turn car before Parking", and the second reads "Do not follow past this point. Allow preceding car to turn before proceding."

The purpose of the first is to allow an orderly departure of cars in any order. The turning space might be full up later, so you had better exploit it now! The car park capacity is increased by a large factor if the cars are parked in a logical sequence. It is known that stupid drivers strive to thwart such logic, and they need to be given firm direction, but that is outside the scope of this document.

The purpose of the second sign is self evident. The provision for turning is for a "three point turn" in a triangular area. There is nothing worse than preparing to do the reverse part of a three point turn and then discovering that there is a car following you at about one metre behind. It is hard to imagine that anyone would drive close behind a car that is obviously just about to reverse, but I have experienced it many times on the driveway at the last house I built. That driveway was also long and windey.

Normally, there is no reason to stop one car following another down the drive. If a second car catches up to the first, this won't matter, as long as she waits at the sign.

This scheme requires some means of detecting a car passing the "Traffic Light" up near the gate. By means of this detection, the system knows that the driveway is occupied by one or more vehicles travelling towards the house.

Indeed car detectors are required at both ends of the driveway. Each of them will have to detect the presence of a car passing over it, and be able to determine the direction of travel. The data from the pair of these detectors will enable the system to know how many cars are on the driveway, if any, and which direction they are travelling.

The reason for keeping track of the number of cars is just so they can be counted off as they leave the driveway (section) so that the "zero cars" (line clear) state is detected.

For Up Hill (Away from the house) traffic, a traffic light is placed just up from the turning triangle. This light will normally be RED. At strategic locations in the yard, near where drivers might enter their car are several push buttons. A press on any of these is a bid for "right of way" up the hill.

If the Red light is flashing, that indicates "Car coming down the hill".

There are two possible system responses to a button push when the red light is flashing.

The first is that the button push is ignored.

The second is that the button push is responded to as soon as the driveway has no cars on it (line clear).

If a driver runs from the house to a car in the rain, but cannot proceed up the drive immediatly, as a car is coming down the hill, she might be pleased to not have to get back out of the car to push a button later.

If a button is pushed, but no car proceeds up the hill, then perhaps the response to the pushing of the button should "time out".

When a button is pressed, the signal at the front fence changes state immediatly, and the traffic light at the top end changes to Flashing Red. When the light changed to Flashing Red, there might have been a down-hill bound car just passing (and just failing to see) the signal, so if after a set delay, no car has passed the detector, the up-hill bound car is given right of way with a green light.

The need for the buttons is unfortunate, but the scheme has to have some guard against cars entering the driveway at both ends at the same instant. There might be satisfactory ways to achieve this without the buttons. Detecting cars well before they reach the signals is a possible approach. In this approach, if cars approach both ends of the driveway simultaneously, then they can both be shown a red light. After a delay for a system confirmation that neither has passed the red light, one light can cange to green as the other changes to flashing red.

A trouble with this is that there is very little space in front of the signals to assign to "early car detection". This is mostly a problem at the house end of the driveway where there might be reasons to move cars around the yard and unnecessary triggering of the signals would be undesirable. Perhaps a push button that is the reverse of the one originally proposed would be better. A "shunting moves only" button.

Another complication is the possibility of moves on the drive where the destination is some point along the drive. In such cases, a car might enter the drive and then change direction of travel before reaching the other end. It might even leave the drive at the same end that it entered from. Of course, this happens often now whilst the house is being built. It is common to leave the house to pick up some item stored half way up the hill and then return to the house site. When such moves are being made, of course the rule that it is ok for one car to follow another will not be allowed to apply. Such moves will not be made by drivers who are unfamiliar with the system, so a requirement that a driver "Switch out the <Following Allowed> Rule" would not be arduous.