Seal versus asphalt

Does the surface of the road influence your choice of where to ride?

Tasmania has a decent number of asphalt roads in good condition for road riding.

Over recent years local and state government have used spray seal, or chip seal, on roads that once had asphalt surfaces.

It’s not hard to see why cyclists prefer asphalt to chip, it’s faster and less prone to flat tyres.

Some riders will use a wider tyre and/or lower pressure when they know they will be riding on spray sealed roads and shoulders..   

The spray seal is cheaper in the short-term than asphalt and is also used to extend the life of asphalt roads. Over the life of a road, asphalt is about two and a half times more expensive than spray seal but needs less maintenance and provides a superior surface. (Orange Council in NSW has a simple description of the comparison between spray seal and asphalt on its website.)

As spray seal is cheaper than asphalt it means that a greater length of shoulders can be sealed, which benefits road riders. However, it does need to be applied in certain weather conditions for the surface to be effective and most durable, otherwise it may be compromised.

But if governments are sealing shoulders to benefit cyclists is spray seal a good choice or should they be using asphalt?

Richmond Road

The state government’s welcomed shoulder widening and sealing of the the Channel Highway through Bonnet Hill and Taroona for cycling has seen asphalt used.

It is a good choice for a road that is highly utilised by bike riders throughout the week.

However, on Richmond Road, another popular cycling route, spray seal is being used to widen and seal shoulders.

The shoulder improvement work will benefit riders, although it’s primarily being done to improve safety on the road for the high number of tourists who drive it.

To begin with the shoulders will be sealed with a 7mm aggregrate chip. This is one of the smallest chips used and should give riders a smooth ride once it is settled in.

A year or two later there are plans to spray seal the entire road with a 14mm aggregate chip, followed by a 7mm chip.

This means that for the coming few years it’s likely that cyclists will end up riding on the road rather than the shoulders.

The spray sealed shoulders will be rougher than the asphalt surface and when the entire road is spray sealed the smoothest route will emerge under car tyre pressure in the main lanes. It may take years before the shoulders are smooth enough to ride on.

Road sweeping

Another problem for cyclists is that chips from the seal are flicked up and away by cars as they drive on it.

This means chips gather at the sides and shoulders of a road and need to be regularly swept for some months as the road settles in.

The Channel Highway south of Kingston was spray sealed not long ago and it left piles of chips sitting in the shoulders, causing inconvenience and danger to cyclists (featured photograph shows Channel Highway shoulder).  

Wide, well sealed shoulders help to provide a separation between cyclists and vehicles. If shoulders are strewn with debris it will push cyclists back on to the road.

Positive provisioning

The state government has a positive provisioning policy that means it will build or retrofit bicycle infrastructure on new and renewed state roads.

When a road or shoulders are being resealed to help cyclists it will choose a 7mm aggregate chip as a compromise between surface quality and cost.

But should the government’s positive provisioning policy go further than using the 7mm chip? Should it identify popular road routes around the state for shoulder asphalting or at the very least, specifications to ensure spray seal is properly swept and rolled to create a surface suitable for cycling?

During the election the government promised to widen and seal shoulders along a stretch of the West Tamar Highway to provide “improved surfaces” for cyclists.

If the Channel Highway and West Tamar Highway can be asphalted, then which other road surfaces around Tasmania should the government recognise for road riders?