Most sites that fail on transport grounds do not fail because of traffic volumes. They fail because the access cannot be made to work.
Visibility that cannot be achieved without land the applicant does not own. A frontage on a road where the authority will not permit a new junction. A geometry that works for cars and not for the refuse vehicle that has to reach the same point.
None of these are difficult to identify. They are just frequently identified after purchase rather than before it.
What an appraisal is looking for
A site access appraisal is a focused piece of work that answers one question. Can a suitable access be formed here, for the development being contemplated.
It examines the frontage and where an access could physically go. Visibility splays in both directions, measured against the recorded speed of traffic rather than the posted limit. Whether the land needed for those splays is within the applicant’s control. The status and classification of the road. Existing constraints such as bus stops, crossings, junctions, trees, lighting columns, drainage and utilities. And whether the access geometry suits the vehicles the development will generate.
It is a fraction of the work of a transport assessment and answers a different question. The assessment asks what the impact will be. The appraisal asks whether the thing is possible.
Visibility is where sites usually fail
Of all the constraints, visibility ends most schemes.
Splays are calculated from the speed traffic actually travels, established by survey rather than assumed from the signed limit. On a rural road signed at 60 with traffic running at 50, the required splay is set by the 50.
The splay then has to be achievable and maintainable. That means clear of obstruction now and in future, which brings in hedges, verges, walls, signs and anything else within the visibility envelope.
The part that catches people is ownership. A splay extending across a neighbouring frontage requires that land or an agreement over it. Without either, the access cannot be delivered regardless of what the drawing shows.
Access geometry has to suit the vehicles
An access that works for a car may not work for everything else that needs to use it.
Refuse vehicles, delivery vehicles and fire appliances all have their own requirements, and the turn into and out of a narrow bellmouth is where problems appear. This is where swept path analysis belongs, at appraisal stage rather than after the layout is drawn.
Where the access serves several units, the width and radii need to allow two vehicles to pass at the point of entry. Where it serves an adoptable road, adoption standards apply from the outset.
What the authority will and will not accept
Some constraints are policy rather than physical.
Certain roads carry a presumption against new accesses. Some authorities require access to be taken from the lowest classification road available. Some require existing accesses to be closed as a condition of forming a new one.
None of this is visible from a site plan. It comes from knowing the local authority’s position, and from asking before rather than after. This is the argument for pre-application engagement, which works best when it starts from a proposition rather than an open question.
Why timing changes everything
The value of an appraisal is entirely in when it happens.
Before an offer, it informs the price or the decision to walk away. Before design, it fixes where the access goes and lets the layout build around it. After planning submission, it tells you what has already gone wrong.
A site bought on the assumption that access is straightforward, which then proves not to be, is difficult to recover. The options narrow to acquiring additional land, redesigning around a compromised access, or abandoning the scheme.
What comes out of it
For most sites the output is short. A plan showing where access can be taken and the visibility that can be achieved, a note on the constraints, and a clear statement of what is deliverable and what is not.
Where there are problems, it sets out what would need to happen. Land to acquire, works to a frontage, a change to where the access is taken, or a scale of development the access could reasonably support.
That last point is often the useful one. An access that cannot serve eighty units may serve thirty perfectly well, and knowing that early shapes the whole appraisal of the site.
Where it fits with everything else
An appraisal is the first piece of transport work, not a replacement for the rest.
What follows depends on scale. A transport statement or assessment, a travel plan, junction modelling, and eventually the Section 278 or Section 38 agreement delivering the works themselves.
All of it rests on the access being deliverable. Getting that settled first means the remaining work is building a case rather than defending an assumption.
Worth doing before you commit
For the time it takes, an appraisal removes the largest single risk on most sites.
Examples across a range of site types are set out in TPA’s project experience.
If you are looking at a site and access is untested, that is the point to ask. You can reach the team through the London office, the Bristol office, the Cambridge office, the Norwich office or the Welwyn Garden City office.
