Could controlled motorways create a safer smart motorway solution?

The response - published last week - says the Department for Transport (DfT) and National Highways "should revisit the case for controlled motorways" and set out how their business case compares with the business case for all lane running (ALR) motorways.

"We will look to publish an initial report which compares the business cases later this year which will be updated once further data is collected on ALR motorways over the next few years," the response adds.

So what exactly are controlled motorways? Controlled motorways add variable and mandatory speed limits to a conventional motorway to control the speed of traffic, while retaining a permanent hard shoulder. Overhead electronic signs display messages to drivers, such as warning of an incident ahead.

Traffic conditions are monitored using vehicle detection equipment, installed in or adjacent to the motorway. The vehicle detection equipment is linked to a Motorway Incident Detection and Automatic Signalling (Midas) system which analyses the data and recognises either queueing traffic or congestion. This allows appropriate signs and mandatory speed restrictions on signals to be set to manage traffic conditions.

The first controlled motorway was introduced in 1995, when mandatory variable speed limits were introduced on the M25 Junctions 10-J15. By the end of 2018, controlled motorways covered 220km of the network (around 3% of the strategic road network).

AA president Edmund King has emphasised that the AA believes "controlled motorways with a hard shoulder are the safest option" and the organisation is "pleased that the business case for these will be examined" as a result of the transport select committee inquiry.

The safety of ALR smart motorways – where the hard shoulder has been replaced by a live lane – has been repeatedly called into question. The transport select committee inquiry launched in March this year, with the committee asked to examine the benefits and dangers of the roads after a further rise in annual deaths.

Overall, the report found that existing safety data on ALR smart motorways is "insufficient".

It added: “In addition, other smart motorway designs, such as controlled motorways and dynamic hard shoulder motorways, have lower casualty rates than ALR motorways. The government and National Highways are taking steps to make ALR motorways safer, but it is too early to judge the effectiveness of those measures.

“In conclusion, we are not convinced that the benefits of ALR motorways are sufficient to justify the risks to safety associated with permanently removing the hard shoulder.”

Figures in National Highways' Smart motorways stocktake first year progress report - published in April last year - do indicate that there were fewer fatal casualties on controlled motorways between 2017 and 2019 than on ALR motorways (see table below).

In 2019, for example, there were five fatal casualties on controlled motorways, compared to nine on ALR motorways.

The progress report also found that fatality rates (per hundred million vehicle miles) on controlled motorways between 2015 and 2019 was lower than on both ALR and dynamic hard shoulder (DHS) motorways (see table below).

The rate was 0.06 for controlled motorways, 0.08 for DHS motorways and 0.12 for ALR motorways.

There were, however, more slight and serious casualties on controlled motorways compared with ALR smart motorways (see table below).

While the DfT will be taking forward all the recommendations set out in the transport committee’s report, it has emphasised that it does not agree with the view that smart motorways were rolled out prematurely or unsafely.

Transport secretary Grant Shapps said he has worked "consistently to raise the bar" on the safety of smart motorways.

"I am grateful to the transport committee and to all those who provided evidence for its work," he said.

“While our initial data shows that smart motorways are among the safest roads in the UK, it’s crucial that we go further to ensure people feel safer using them."

Like what you've read? To receive New Civil Engineer's daily and weekly newsletters click here.