Any project that adds a new access point, junction, or significant volume of traffic onto a national road in Kenya will run into the term Traffic Impact Assessment, or TIA, at some point in the approval process. Most people encounter the term in a permit condition or a KeNHA letter, with no real explanation of what it means or why it applies — it sits between traffic engineering and permitting, and rarely gets covered by someone fluent in both.

This article covers what a KeNHA TIA actually requires, when you need one, how it fits into the access permit process, and what a competent report needs to contain. A downloadable checklist is included at the end so you can check your own submission against KeNHA’s requirements.

What a Traffic Impact Assessment Is

A Traffic Impact Assessment is a technical study that quantifies how a proposed development or access point will affect traffic flow, capacity, and safety on the surrounding road network. The core question it answers: once this access point is in use, will the road and junction still function safely and within capacity — and if not, what needs to change?

For projects on national roads, KeNHA requires the TIA as a mandatory part of the Roadside Development Control (access road and way leave) permit application. It isn’t an optional supporting document. Applications submitted without one, or with one that doesn’t meet KeNHA’s data requirements, are routinely returned for revision, which is one of the most common causes of delay we see on client projects.

When You Need One

KeNHA requires a Traffic Impact Assessment as part of the application for approval of roadside developments, most commonly for:

  • New access roads or driveways connecting a commercial, industrial, or large residential development to a Class S, A, B, or C road
  • Petrol stations, shopping centres, warehouses, factories, and other developments expected to generate significant additional traffic
  • Junction modifications or new junctions on or near a national road
  • Any development where the change in traffic volume or turning movements could affect the safe operation of the adjoining road

If your project only involves a low-traffic residential access point, the scope of the TIA required will typically be lighter, but KeNHA still expects supporting traffic data as part of the application. It’s worth confirming the expected scope with your regional or corridor office before you commission the study, rather than after.

What KeNHA’s TIA Requirement Actually Covers

KeNHA’s published service standards for approval of roadside developments set out specific technical content the TIA report must contain. At minimum, this includes:

  • Average Daily Traffic (ADT) data with a 10-year projection. The report must capture current traffic volumes on the affected road and project how they will grow over a 10-year horizon, not just describe existing conditions.
  • A letter from the Regional Director or Corridor Director for the road section in question, authorising the study and confirming it has been reviewed at the regional level.
  • Junction and turning movement analysis. For Class A roads, KeNHA requires a holding lane for right-turning traffic as standard. For Class B roads, whether a holding lane or other junction treatment is required is determined by the findings of the TIA itself, rather than being fixed in advance.
  • Engineer sign-off. The TIA report must be signed and submitted by a professional engineer, with the engineer’s current practising licence attached. An otherwise complete report without this will be rejected.

This TIA data is submitted alongside the wider set of access permit documents (survey maps, engineering design drawings, geo-referenced site plans, and cross-sections), not as a separate application. Our companion guide on KeNHA Access Permit Requirements covers the full document set and the online application process end to end.

How the Assessment Is Actually Carried Out

The technical content KeNHA asks for reflects a standard traffic engineering process, even though the service charter only states the outputs. In practice, a TIA that will pass review is built through the following stages:

1. Data collection. Traffic counts are taken at the site and at the key junctions likely to be affected, typically covering weekday morning and evening peak periods, and a weekend peak where relevant. Existing road geometry, speed data, and crash history (where available) are recorded alongside the counts.

2. Trip generation. The additional traffic the proposed development or access point will generate is estimated, based on the type and scale of the development. Established trip generation rates for similar land uses are used where local data exists; where it doesn’t, trip rates are built up from first principles and the assumptions are clearly documented.

3. Trip distribution and assignment. The generated trips are distributed across the surrounding road network based on likely origins and destinations, then assigned to specific routes and turning movements at each junction under consideration.

4. Capacity analysis. Each affected junction and road segment is analysed under three scenarios: current conditions, the future horizon year without the development, and the future horizon year with the development. This shows whether the added traffic pushes any junction past an acceptable level of service.

5. Mitigation design. Where the analysis shows a junction or road segment will be pushed beyond acceptable capacity or introduces a safety concern, the report proposes specific mitigation, a holding lane, a taper extension, signal timing changes, or a roundabout, sized to bring performance back within an acceptable range.

6. Reporting and sign-off. The findings, data, assumptions, and drawings are compiled into the TIA report, signed by the responsible professional engineer, and submitted with the access permit application.

Common Pitfalls

Treating the TIA as a formality rather than a design input. A TIA commissioned after the access design is finalised often reveals a problem that requires redesign, costing more time than doing the study first.

Under-scoping the traffic counts. Counts taken on an atypical day, or missing a relevant peak period, produce an ADT and capacity analysis that doesn’t hold up to scrutiny and gets challenged at review.

Missing the 10-year projection. A TIA that only presents current-year traffic, without the 10-year growth projection KeNHA specifically asks for, is incomplete on submission.

No holding lane provision on Class A roads. Because this is a fixed requirement rather than something the TIA determines, designs that omit it get sent back regardless of what the traffic analysis shows.

Submitting without the engineer’s practising licence attached. A technically sound report can still be rejected on a documentation technicality if this is missing.

How Strasan Group Helps

Our transportation engineering team carries out Traffic Impact Assessments as part of the design process for access roads, junctions, and roadside developments, not as an afterthought bolted onto a finished design. That means traffic data and capacity analysis inform the access layout from the start, rather than forcing a redesign after the fact.

Where the TIA is being prepared for a KeNHA submission, our road safety audits and KeNHA access permit service pairs the traffic study with an independent safety review and manages the permit submission itself, so the report that reaches KeNHA’s reviewers is complete on the first pass.

Downloadable Checklist

To help you track your submission, we’ve put together a one-page checklist covering KeNHA’s TIA and access permit documentation requirements. Download it below and use it to confirm your application is complete before you submit.

Download: KeNHA TIA & Access Permit Checklist (PDF)

If you’d like our team to review your traffic data or scope a TIA for an upcoming project, get in touch before you finalize your access design. Catching a capacity issue on paper is far cheaper than catching it after construction.