Highway bonds, commuted sums and who pays
A bond secures completion of an adoptable road and comes back; a commuted sum buys future maintenance and does not. How both are calculated and negotiated.
A highway bond is security the highway authority holds against the risk that you do not finish the road. It is required under a section 38 agreement for new streets the authority will adopt, and under a section 278 agreement for works to an existing highway, both under the Highways Act 1980. A commuted sum is different. That is a capital payment covering future maintenance of something the authority would not otherwise accept, and unlike the bond you never get it back.
What a bond secures and why it exists
The authority is being asked to take on a road in perpetuity. It wants the road built to its specification before it does so, and it has no contractual relationship with your contractor.
So it takes security. If the development stalls, the developer fails, or the works are abandoned half finished, the authority can call the bond and use the money to complete the street to adoptable standard. That protects the authority, and it also protects the people who have bought houses on a street with no surfacing and no street lighting.
Bonds also exist to protect frontagers through a separate mechanism. The advance payments code in sections 219 to 225 of the Highways Act 1980 requires a payment or security to be deposited before building work starts on a new street, with exemptions including where a section 38 agreement with adequate security is already in place. In practice entering the section 38 agreement is how most developers deal with it.
How the bond figure is calculated
The bond is based on the estimated cost of completing the works, not on the value of the development. The authority prices the road, the drainage, the lighting, the footways and the structures from your approved engineering drawings.
Three elements usually sit on top of the raw construction estimate.
- An allowance for the authority's own supervision, administration and design-check costs.
- An uplift for inflation and for the cost of procuring the works at short notice if the bond is called.
- Retention of a proportion through the maintenance period, even after substantial completion.
Figures vary between authorities and are set in their published section 38 and section 278 procedures, so take the rate from the authority rather than from a general assumption. What is negotiable is the estimate itself. A bond priced off an outdated cost schedule, or including works that have already been built and inspected, is worth challenging with your engineer's own build-up.
The bond is usually provided as a surety bond from an insurer or a bank guarantee, with a cash deposit as the fallback. A surety bond costs an annual premium, which is a real holding cost on a slow-moving scheme and belongs in the cash flow rather than in a footnote.
Commuted sums for non-standard features
A commuted sum is the price of asking the authority to maintain something that costs more than its standard detail. It converts a future maintenance liability into a single payment now.
| Feature | Why a commuted sum is sought |
|---|---|
| Block paving, setts or coloured surfacing | Higher maintenance cost than bituminous surfacing |
| Trees in the highway or in verges | Pruning, inspection, eventual replacement, root damage risk |
| Drainage features in the highway, including gullies and permeable surfaces | Non-standard cleaning and replacement regimes |
| Structures such as retaining walls, bridges and culverts | Inspection regimes and long-term renewal |
| Street lighting above standard specification | Non-standard columns, bespoke parts |
| Traffic signals and crossings created by a section 278 scheme | Energy, maintenance and renewal of equipment |
The sum is normally calculated as the maintenance and renewal cost over a defined period, commonly several decades, discounted or not depending on the authority's method. Ask for the calculation. Two authorities can produce sums that differ by an order of magnitude for the same tree, and the only way to test it is to see the inputs.
The design decision follows the sum. Where a commuted sum for a feature exceeds what the feature contributes, the honest answer is often to redesign or to keep the feature in private ownership on a managed estate. That has its own costs, including a management company and an estate charge the purchasers will eventually question. Our note on highway drainage, gullies and who maintains them covers that choice in more detail.
Release, and the maintenance period
The sequence is construction, provisional certificate, maintenance period, final certificate, then adoption and bond release.
The provisional certificate is issued when the works are substantially complete to the authority's satisfaction. The maintenance period then runs, during which the developer remains responsible for defects, and it is commonly twelve months although authorities set their own. At the end, the authority inspects, you remedy any defects, and the final certificate triggers adoption and release of the remaining bond.
Two practical traps. First, the maintenance period does not start until the certificate is issued, and getting it issued requires a complete set of records, test results and as-built drawings, so the paperwork delays bond release more often than the construction does. Second, the period runs on the condition that the street remains undamaged, and a later phase of construction traffic chewing up a completed road can restart the clock.
Partial or phased release is worth negotiating at the outset on a large site. Adoption of phase one, with its share of the bond released, improves the cash position materially.
Insolvency and partly built roads
This is the scenario the system is built for, and it still goes wrong.
When a developer fails mid-build, the authority calls the bond, but the bond covers the cost of completion as estimated at the time it was set. If three years of inflation have passed, or the part-built road has deteriorated, or the drainage was never tested, the money may not stretch. The residents are then living on a private street with no adopting authority.
For anyone buying into a part-complete site, the questions are whether a section 38 agreement exists, whether the bond is live and for how much, whether a provisional certificate has been issued, and whether the advance payments code deposit was made. Our note on car club bays and keeping them viable deals with the related problem of maintaining a committed facility after the developer has gone.
Getting bonds into the appraisal
Bonds and commuted sums are frequently missed or understated in development appraisals, and they are not small on a scheme with a spine road.
Four cost lines to carry. The bond premium or the opportunity cost of a cash deposit, annually until release. The commuted sums, as a one-off at the point the agreement is signed. The authority's fees for checking and supervising the works, which are charged separately. And the cost of the works themselves, which is the largest item and the one most often priced before the authority has commented on the specification.
Programme matters as much as cost. Bond release two years after practical completion of the houses is normal, and an appraisal that releases it at completion of the last plot overstates the return. Where highway works are a material part of the scheme, the Viability Assessment should show them explicitly rather than inside a contingency, and the junction and access design behind the figures belongs in the Transport Assessment.
Agree the specification before you price the bond. Most disputes about bond value are really disputes about whether a particular detail is adoptable, and those cost far less to settle on a drawing than on site.
This is general guidance, not legal advice, and bond and commuted sum requirements should be confirmed with your local highway authority before relying on them. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
What is the difference between a highway bond and a commuted sum?
A bond is security against the risk that the works are not completed to adoptable standard, and it is released after the maintenance period ends and the final certificate is issued. A commuted sum is a capital payment covering the future maintenance of a non-standard feature the authority would otherwise refuse to adopt, and it is not returned.
How is the bond figure arrived at?
From the estimated cost of completing the highway works taken off the approved engineering drawings, usually with allowances for the authority's supervision and administration costs and an uplift for inflation and short-notice procurement. The estimate is negotiable where it is based on outdated rates or includes works already built and inspected.
How long is the maintenance period before a bond is released?
Commonly twelve months from the provisional certificate, although authorities set their own periods. The period does not begin until the certificate is issued, which requires complete records, test results and as-built drawings, so administration delays release more often than construction does.
Which features typically attract a commuted sum?
Block paving and decorative surfacing, trees in the highway or verge, non-standard drainage including permeable surfaces, structures such as retaining walls and culverts, street lighting above the standard specification, and signals or crossings created by a section 278 scheme. Ask for the calculation, because methods and periods vary widely.
What happens to a part-built road if the developer fails?
The authority can call the bond and use it to complete the street, but the bond was sized when the agreement was signed, so inflation, deterioration and untested drainage can leave a shortfall. Buyers on a part-complete site should check whether a section 38 agreement exists, whether the bond is live and whether a provisional certificate was issued.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.