Slow vehicle bays which are shown in Figure 4‑2, are the formalised use of very short lengths of widened, unobstructed sealed shoulder on two-lane rural roads to allow slow moving vehicles to pull out of a traffic lane to permit following vehicles an opportunity to pass. Drivers of vehicles in slow vehicle bays do however have to ensure that their way is clear before they can re-enter the traffic lane.
Slow vehicle bays are often colloquially referred to as passing bays. However, in legislation, a passing bay is a space provided for opposing vehicles to pass one another on narrow two-way roads. Slow vehicle bays are provided to allow vehicles travelling in the same direction to pass.
Figure 4‑2: Slow vehicle bay located on State Highway 75
Slow vehicle bays are short when compared to passing lanes, usually less than 300m. On roads with lower traffic volumes, they can provide some of the benefits of passing lanes.
To avoid driver confusion, slow vehicle bays and passing lanes should not be closely interspersed along a section of road. To maximise the use of slow vehicle bays they should be located where the drivers of slow-moving vehicles are able to use them without adding unacceptable delays to their total journey time.
Unless the conditions in the application and location section (see below) are all met, short lengths of widened shoulder on two-lane rural roads are to be marked and signed as conventional, but short passing lanes because motorists are more familiar with them. Refer to the passing lanes for details.
Refer to Austroads Guide to Road Design Part 3: Geometric Design (Austroads GRD: Part 3) for advice regarding where slow vehicle bays may be appropriate
Austroads Guide to Road Design Part 3: Geometric Design (Austroads GRD: Part 3)(external link)
Slow vehicle bays are rarely used by trucks, except on very steep grades where the trucks are reduced to crawl speeds. Slow vehicle bays are more suited to recreational and tourist routes where drivers of slow vehicles are usually more willing to let faster vehicles past.
The provision of slow vehicle bays may be considered on winding two-lane rural roads in mountainous, coastal and scenic areas where most of the following conditions are met:
Where practicable, a series of slow vehicle bays (not closely interspersed) should be provided to give regular passing opportunities.
The development of proposals to provide slow vehicle bays should include careful consideration of traffic flows and their composition, the need to minimise queue lengths, minimum sight distance requirements and the relative costs and benefits of providing other types of passing opportunities.
Ideally, slow vehicle bays should be located so they end at the crests, or on the down sides, of hills. It is essential that they do not end abruptly just prior to, or just beyond, blind horizontal curves or just over the crests of hills, ie where drivers do not have an adequate view of a slow-moving vehicle re-entering the traffic lane immediately ahead of them.
Similarly, drivers of vehicles exiting from slow vehicle bays should have a clear view of vehicles approaching from behind.
Where slow vehicle bays are located on a sustained grade they should be sufficiently long, or located frequently enough, to reduce the probability of slow-moving vehicles having to stop completely to allow following queued vehicles to pass.
There are advantages in locating slow vehicle bays on right hand horizontal curves, when sight distance requirements can be met, because passing vehicles have shorter distances to travel and there is better inter-visibility between vehicles. It is not advisable to locate slow vehicle bays on left hand horizontal curves because passing vehicles will have longer distances to travel and poor inter-visibility between vehicles.
Preferably, slow vehicle bays should not be located in the vicinity of parking areas, rest areas and scenic outlooks. When they are, great care should be taken with signs and markings to ensure that slow vehicle bays are clearly distinguished from other trafficable areas.
For the types and location of signs used for slow vehicle bays refer to Table 4‑4. The correct signs are necessary to maximise the use of slow vehicle bays and to ensure safe and efficient traffic operations.
Table 4‑4: Slow vehicle bay signs
| Sign code | Example | Description/use |
|---|---|---|
|
A42-3 Slow vehicle bays next ‘[distance] km’ |
 |
An A42-3 sign may be installed in advance of a series of slow vehicle bays. The sign should be located at least 100m in advance of the A42-4 sign for the first slow vehicle bay in the series. |
|
A42-4 Slow vehicle bay ‘[distance] m’ |
 |
An A42-4 sign should be installed approximately 300m in advance of each slow vehicle bay. |
|
A42-5 Slow vehicle bay indicator |
 |
An A42-5 sign should be installed 15m in advance of the start of each slow vehicle bay. |
| W13-1 (L)
Road narrows – left side |
 |
W13-1 (L) signs should be installed at the start of the merge taper. |
Slow vehicle bays should be marked as specified below and as shown in Figure 4‑3.
Edgelines, including the entry and exit tapers, should be marked as described in the edgelines section.
Edgelines
Table 4‑5: Slow vehicle bay edgeline marking
| Application | Edgelines, exit and entry tapers for slow vehicle bays |
|---|---|
| Colour | Reflectorised white |
| Width |
100mm minimum. Exit taper may be increased to 150-200mm |
| Stripe | Continuous |
| Length | N/A |
| Location | N/A |
A continuity line marking is used to define the edge of the through traffic lane adjacent to a slow vehicle bay. The line is marked for the full length of a slow vehicle bay excluding the exit taper, as indicated in Figure 4‑3. Continuity lines should be marked as described in Table 4‑6.
Table 4‑6: Slow vehicle bay continuity line markings
| Colour: | Reflectorised white |
|---|---|
| Width: | 200mm minimum |
| Stripe: | 1m dash, 3m gap |
The following centre-lines should be marked on sections of road where slow vehicle bays are provided:
A no-passing line may also be marked in the opposite direction if the standard criteria are met.
The delineation of slow vehicle bays should be equivalent to, or better than, the delineation of the roads on the approaches to the bays, so that night time delineation for drivers is not adversely affected.
The normal delineation requirements for slow vehicle bays on state highways are specified below.
The delineation provided on some rural roads may be to a lesser standard than that specified for rural state highways. The delineation standard for slow vehicle bays on these roads should match the standard of delineation provided on the approaches to the bays.
If using Type ‘A’ edge marker posts, as detailed in the edge marker posts,
Edge treatments - Edge marker posts
Treatment of curves - Edge marker posts
they should:
An example layout is shown in Figure 4‑3.
Red retroreflective raised pavement markers (red RRPMs) may be used to define the left edge of slow vehicle bays, but only when it is not possible to install edge marker posts:
Figure 4‑3: Markings and signage for slow vehicle bays
