Bypass fog: the appendices

In autumn 2017 Stockport Council published a Strategic Outline Business Case for building the A555 extension to Bredbury (aka A6-M60 Bypass). A few weeks later a lengthy set of appendices appeared. Although the Appendices were largely ignored at the time, they do contain important information.

The main volume of the Business Case (Volume 1) said nothing about what would happen beyond the Bypass’s opening year. The Appendices reveal a possible reason for that reticence: the Bypass would do nothing to stop Stockport’s road junctions becoming gummed up by 2039.

Perhaps even more worryingly, the Appendices maintain the silence of Volume 1 over how the Bypass itself will perform. If this information is regarded as so unhelpful it cannot even be tucked away in the Appendices, then there may well be a problem.

In fact, the problem with the operation of the Bypass itself can be readily deduced from the Appendices. If the junctions on Stockport’s other major roads become increasingly gummed up by 2039, the Bypass’s own junctions are highly likely to go the same way. The current design includes five junctions with traffic-lights on the main carriageways!

If, as seems likely, junctions on the carriageways are not viable in the longer run, then the statement in Business Case (Volume 1) that the Bypass junctions have been judged able to operate “within acceptable parameters” (page 38) in the opening year (page 89) is downright misleading. But if the traffic-signal controlled junctions of the current Bypass design were to be replaced by motorway-style junctions with slip roads, the destructive physical impact of the three junctions in Offerton on local residents and their environment would be dramatically increased.

A report to the Council’s Executive in October 2003 about a combined SEMMMS road M56-M60 is relevant. It said that by the 15th year of operation, the traffic-signal controlled junctions would become congested, but if they were replaced by motorway-style junctions, the resulting faster road would become overloaded with traffic sucked in from the motorways. We have a solution for Stockport Council: don’t build it!

The Business Case has another major short-coming: it has not modelled the traffic that will be “induced” by the construction of the Bypass. A recent independent study carried out for the Campaign for the Protection of Rural England found an average 47% extra traffic over 20 years on the road schemes it studied – both motorways and bypasses. The A6-M60 Bypass and other affected local roads would manifestly be unable to cope with such a level of induced traffic.

As Councillor Sheila Bailey told the Council’s Cabinet on Tuesday (14th November): “It won’t work!” The Bypass would cost £500 million for only 8.5 metres of road and devastate our cherished Lower Goyt Valley and green spaces – while reinforcing our traffic problems.

The Bypass is designed to improve the connection from the motorway to Stockport’s southern borders, so it will encourage development on the green belt and the construction of more car-dependent housing estates.

The traffic modelling for the Business Case has assumed a growth in traffic. This should not be regarded as inevitable. From year 2000 to 2015, traffic declined on the A6 by 12% and on the A627 by 4% (DfT Traffic Counts). Increases in traffic may result from development decisions that increase car dependency. Constructing the A6-M60 Bypass would be such a decision on a grand scale.

The main points of our analysis of the Appendices of the Business Case are set out below.

 Silence about the Bypass itself: why?

Neither the Appendices nor the Business Case itself offer more than a scrap of information about how the A6-M60 Bypass itself would perform. Why didn’t the authors of the Business Case and the Appendices want to tell us about how well the Bypass will work? Instead we have a worrying silence.

Torrent of “induced traffic” ignored

Appendices 6-9 (page 261) confirm that the Business Case used fixed matrix forecasting for traffic. This is incapable of predicting new journeys “induced” by the Bypass. A recent independent study for the Campaign to Protect Rural England found that on average traffic on new roads grew by 47% more than other roads in their region over 20 years.

Broken tunnel – broken promise

The Tunnel Option Review (Appendix 5) reveals a technical impediment to the promised tunnel through Lower Bredbury. A tunnel would largely shield neighbouring residents from noise and fumes. Two shorter tunnels appear more feasible than a single long tunnel but would expose the locality to loud traffic noise bursting from the gap between the tunnels.

Queuing to double?

The Traffic Impact Report (Appendices 6-9, page 240) forecasts that “permanent queuing” will double in Stockport by 2039 – with or without the Bypass. If this is true, the Bypass has no answer to Stockport’s congestion. The forecast doubling of queuing could be even worse because of the impact of induced traffic which could affect some major roads as well as the Bypass. We need transport solutions that do not foster car dependency.

Minimal time savings in opening year

On 31 routes listed in the Traffic Impact Report (Appendices 6-9, page 239) the Bypass delivers an average time saving of 1.2% per route in its opening year – maybe 40 seconds. The Business Case set a target of a 20% reduction in time between Hazel Grove and Bredbury in the opening year (A627, A6017). The Traffic Impact Report shows nothing like such a saving.

Increased traffic at Dan Bank, Marple

Analysis of figures in Appendices 6-9, page 246 show that traffic through Dan Bank, Marple will increase despite a diagram in the Business Case (page 46) showing a reduction in the opening year. This must cast doubt on other elements of the diagram – which was the only information about traffic volumes provided by the Business Case (Volume 1) apart from a short list of roads that would experience changes.

Restricted area for “economic benefits” rating

The “very high value for money” rating bestowed on the Bypass by the Business case could be important for applications for further funding.  The Bypass only creeps into the “very high” category, so any overstatement of benefits could have a significant effect. The area within which so-called economic benefits have been calculated excludes some places – Disley, New Mills, Macclesfield – which might suffer congestion as a result of the Bypass scheme (Appendix 8, Local Model Validation Report). This omission could have affected the rating. Failure to model for induced traffic would also have inflated the rating.

Flawed traffic modelling

The Business Case was previously known to have used out-of-date survey information in its traffic modelling. Appendix 8 (The Local Model Validation Report) adds a further detail: the information was augmented by large volumes of mobile phone data. There are drawbacks with this technique (for instance, it is unable to distinguish between people in a car or a bus). Another significant weakness in the modelling is that it was carried out before the opening of A6MARR (Airport Relief Road).  A6MARR will have a profound impact on local roads. The modelling of the  Bypass has attempted to take account of A6MARR but will not be able to achieve a completely accurate picture.