Smart motorway comparison report: December 2022
Published 15 December 2022
Applies to England
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Introduction
In 2021, the Transport Select Committee undertook an inquiry into the Rollout and safety of smart motorways. A number of expert witnesses expressed a clear preference for more controlled motorways and the committee noted that in terms of safety, controlled motorways have the lowest casualty rates of the different types of smart motorways based on safety data contained in the Smart motorways stocktake – first year progress report (PDF).
This led to the committee, in its report, making the following recommendation:
The department and National Highways should revisit the case for controlled motorways. The department should set out how the business case for controlled motorways compares with that for all-lane running motorways.
In January 2022, the government confirmed in its response that it would be taking forward all of the committee’s recommendations. This included revisiting the case for controlled motorways and how it compares with all lane running (ALR) motorways and would look to publish an initial report in 2022 which will be updated once further data is collected on ALR motorways over the next few years.
This initial report provides a predominately high-level qualitative summary of information already available related to smart motorways.
Overview
The report seeks to compare 3 types of smart motorways:
- all lane running (ALR)
- controlled (including stretches of controlled motorways which have also been widened)
- dynamic hard shoulder running (DHS)
The report is not a business case and no inference should be made on any considerations about the future of smart motorways. Instead, it seeks to present a high-level view of the position of each smart motorway type as based on published information.
This initial report is part of ongoing work, in response to the Transport Select Committee’s recommendations, to collect and present evidence and evaluation to enable the government to make informed decisions about enhancing capacity on the Strategic Road Network (SRN).
The government has committed to examining existing operating regimes as well as considering if there are any alternative options for enhancing capacity on the SRN. The body of evidence will be further developed over time, for example, through the publication of further Post Opening Project Evaluation (POPE) reports as well as the next set of safety data in 2023.
This report provides:
- a summary of the different types of smart motorways and their features, setting out in more detail when and why each smart motorway type was introduced
- a high-level summary of the impact of each type of smart motorway when considered through a safety, capacity and environmental lens
- a summary of the current understanding on the economics of smart motorways as well as an overview of safety data
Smart motorway types and features overview
This section sets out the different types of smart motorway, when they were introduced and the proportion of the motorway network that was a particular smart motorway type at the end of 2020. It also provides an explanation of the features that are used to operate and are in place as of October 2022 for types of smart motorway.
Controlled Motorways
Controlled motorways retain the conventional motorway configuration, including retaining the hard shoulder but have additional technology such as variable and mandatory speed limits to control the speed of traffic, and overhead electronic signs to display messages to drivers. Controlled motorways alone do not provide additional capacity however in some locations controlled motorways have also been widened to provide an additional running lane.
Dynamic Hard Shoulder (DHS) Running Motorways
DHS motorways apply controlled motorway technology described above but temporarily increase capacity by utilising the hard shoulder as a running lane at peak times. DHS motorways also have emergency areas (EAs) providing a safe place to stop in an emergency, set away from the carriageway.
All Lane Running (ALR) Motorways
ALR motorways apply controlled motorway technology as described above but permanently convert the hard shoulder as a running lane, increasing capacity. ALR motorways also have emergency areas and stopped vehicle detection (SVD) technology
Table 1 Smart motorway types
| Type | Date introduced | Length and proportion of motorway network |
|---|---|---|
| Controlled motorways | First controlled motorway was introduced on the M25 between Junctions 10 and 15 in 1995. | 138 miles, making up 7.2% of the motorway network |
| Dynamic Hard Shoulder (DHS) Running motorways | First DHS motorway was trialled on the M42 between Junctions 3a and 7 in 2006. | 63 miles, making up 3.3% of the motorway network |
| All Lane Running (ALR) motorways | The first ALR motorway was introduced on the M25 between Junctions 5 and 7 and Junctions 23 and 27 in 2014 | 168 miles, making up 8.8% of the motorway network |
Table 2 Smart motorway features
| Feature and description | Controlled motorways (including sections that have been widened) | DHS | ALR |
|---|---|---|---|
| MIDAS (motorway detection and automatic signaling) which identifies queuing traffic or congestion by monitoring traffic speed and flow | Yes | Yes | Yes |
| Overhead electronic signs and signals to display variable mandatory speed limits, Red-X lane closures and information to drivers, such as warning of an incident ahead. | Yes | Yes | Yes |
| Enforcement cameras to deter the minority who break speed limits and ignore Red X signs. | Yes | Yes | Yes |
| CCTV cameras that National Highways operators can move and zoom to monitor and manage congestion and incidents, where notified. | Yes | Yes (DHS have additional fixed CCTV to enable operators to check the hard shoulder ready for opening and closing as a live traffic lane.) |
Yes (On ALR the system has the ability to see 100% of the carriageway.) |
| Emergency areas to stop in an emergency that are clearly signed and orange-coloured, set back from the road and with telephones linking directly to control rooms. | No (Controlled motorways have a hard shoulder.) |
Yes | Yes |
| Stopped vehicle detection technology which can identify a stopped vehicle and alert National Highways control rooms, at the same time setting warning signs of a reported obstruction whilst the alert is verified by an operator. | No | No | Yes |
Smart motorway comparison of impacts
This section sets out information comparing the impact of each type of smart motorway when considered through a safety, capacity and environmental lens. All comparisons in Table 3 are made against a non-smart motorway baseline.
For safety impact, the metrics reflect the latest safety performance available for each road type as published in Smart motorways stocktake – second year progress report.
It should be noted that this report does not take into account any safety benefits due to traffic moving from the local road network to the safer SRN. For expected capacity impact, enhancements reflect the addition of physical space on the road to accommodate current or future congested traffic. For expected environmental impacts, these include all aspects of noise, air quality, landscape, biodiversity and carbon emissions during construction and operation.
Table 3 Incidents per hundred million vehicle miles (hmvm)
| Type of motorway | Personal Injury Collisions (PIC) | Fatal and Weighted Index (FWI) | Killed and Seriously Injured (KSI) |
|---|---|---|---|
| Controlled (with widening) | 8.46 | 0.32 | 1.3 |
| Dynamic Hard Shoulder (DHS) | 7.92 | 0.32 | 1.17 |
| All Lane Running (ALR) | 6.24 | 0.33 | 1.38 |
Conventional motorways PIC per hmvm is 6.12; FWI per hmvm is 0.37; KSI per hmvm is 1.45
This data is not available for controlled motorways without widening as most controlled motorways have widening in place.
Table 4 Expected capacity impact and expected environmental impact
| Type | Expected Capacity Impact (Scheme-specific evidence may be influenced by local considerations) | Expected Environmental Impact (Scheme-specific evidence may be influenced by local considerations) |
|---|---|---|
| Controlled (without widening) | Slight beneficial impact due to minor enhancements from speed management | Slight adverse impact, including no significant land take for construction |
| Controlled (with widening) | Large beneficial impact due to additional lane capacity from widening and minor enhancements from speed management | Significant adverse impact including significant land take for additional lane construction |
| Dynamic Hard Shoulder (DHS) | Moderate beneficial impact due to additional lane capacity by using the hard shoulder at peak times and minor enhancements from speed management | Slight adverse impact including no significant land take for construction |
| All Lane Running (ALR) | Large beneficial impact due to additional lane capacity by permanently converting the hard shoulder into a running lane and minor enhancements from speed management | Slight adverse impact including no significant land take for construction |
Smart motorway economics
National Highways publish post opening project evaluations (POPEs) for all individual smart motorway schemes using data available 1 year after opening and 5 years after opening.
POPEs consider the scheme impact in key areas, including journey reliability, safety and on the environment. The evaluation provides an early mechanism to ensure the project is on track to deliver the anticipated benefits over the lifecycle of a project, which is typically 60 years after opening.
Currently most POPE evaluations for ALR motorways are 1 year after opening and therefore only provide an indication of how each scheme is performing within its first year of operation.
POPE evaluations for 5 year after opening will become available over time and will be able to suggest whether scheme objectives have been met. In addition, because most controlled motorway schemes were associated with road widening, there is currently insufficient information to disaggregate the benefits and therefore compare the smart motorway elements on a consistent basis with ALR and DHS motorways.
Of the 7 DHS motorways, 5 have published 1 year POPEs and, of these, 2 have published 5 year POPEs. Emerging results indicate they are overall delivering safety benefits but, whilst providing additional capacity, speed restrictions required to operate dynamic hard shoulders may have increased journey times. DHS motorways are more cost effective than traditional widening and lead to reduced impacts during construction, especially to local communities.
To date 6 one year POPEs have been published for ALR motorways. Published POPE evidence shows the majority of ALR motorways have shown an improvement in the Personal Injury Collisions (PIC) over time. Only one indicates the rate of improvement may have been greater if the road had remained a conventional motorway, but this is not a statistically significant difference and is only indicative at one-year after. All other schemes show a greater saving in PIC rates over time than if they would have remained a conventional motorway.
Find POPE reports for before 2020 on this page.
Smart motorway safety
The Department for Transport and National Highways have published comparative safety data over the last few years and will continue to build and release further data as we respond to the Transport Select Committee’s recommendations.
It is important to acknowledge that comparing safety metrics across road types is only one element of the analyses undertaken for road safety. Additionally, National Highways undertake:
- intervention data monitoring and evaluation – understanding whether implemented actions are effective and/or achieve their outcomes
- before vs. after analysis – undertaking POPEs to capture the safety benefits from traffic transferring from less safe roads to the SRN
- customer research – understanding what impacts driver experience
- safety reviews – understanding which road type elements are important for mitigations or future road development
Based on the metrics presented in the Smart motorways stocktake – second year progress report in May 2022, the latest data (2016 to 20) shows that, overall, in terms of serious or fatal casualties, smart motorways (all types) are the safest roads on the SRN.
When accounting for traffic flows, safety metrics for all roads on the SRN, including smart motorways, have stable or improving trends over time.
It is important to note that due to the lag time of data availability, the impact of safety measures delivered in the last couple of years are not yet reflected in the latest data.
Most SRN collisions occur between moving vehicles and all smart motorways perform better than conventional motorways on the casualty-focused FWI and KSI rates. Stopped vehicle collisions are a very small proportion of collisions across all roads. Whilst rare, the rate of stopped vehicle collisions resulting in a fatal or serious injury is greater for smart motorways without a permanent hard shoulder (ALR/DHS), but the risk of a collision involving only moving vehicles is lower on these roads.
The department will continue to work with National Highways and the Office for Rail and Road to collect and further improve safety data and insight to better understand safety on the smart motorway network. National Highways will publish its third Smart motorway stocktake report in 2023.