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Evaluate a proposed skyscraper by comparing future transportation conditions with and without the project, then measure its effects on roads, transit, walking, cycling, parking, and curb access. There is no universal trip threshold or congestion metric for every tower: the right study depends on the local rules, the site, the building’s uses, and the capacity of nearby networks.
Start with the decision the study must support
A transportation impact assessment should be scoped with the planning authority and relevant road and transit operators before design is fixed. Its purpose may be to inform approval, identify needed changes to the site plan, or establish mitigation and monitoring requirements.
Agree on the project program and size, construction or occupancy phases, study area, analysis periods, forecast years, and the transport operators whose networks may be affected. Include office, residential, hotel, retail, and other uses separately where their travel patterns differ. UK national guidance says the scale and detail of a Transport Assessment should be proportionate to local circumstances; TxDOT likewise leaves the final methodology to the applicable project manager. These are jurisdiction-specific approaches, not a universal procedure. UK Transport Assessment guidance was revised in 2014, so check current national policy and local requirements before applying it. TxDOT’s Traffic Impact Analysis procedures describe the agency’s own process.
Establish a baseline and a realistic future without the tower
Describe current conditions across modes
Document representative conditions on the streets and transit services likely to be affected. The baseline should cover traffic volumes and operations at important links and intersections, transit routes and service levels, passenger capacity information where available, walking and cycling connections, site access, parking, curb use, and relevant safety conditions. Include normal conditions and recurring peak or special periods when they matter to the project.
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The UK guidance calls for consideration of all-mode travel characteristics, public transport provision, flows, safety history, parking, environmental effects, and committed development. A single count taken at an unusual time is not a reliable picture of typical conditions; explain the data dates and any limits on representativeness. The guidance’s scope and assessment topics provide a jurisdiction-specific example.
Forecast the no-build case
Do not treat today’s network as the future baseline. Add relevant committed development and planned transport changes to create a future background, or “no-build,” scenario for the agreed forecast years. The authority and operators should help determine which projects have enough certainty to include and which network changes are expected to proceed. This prevents ordinary growth or already-planned improvements from being incorrectly credited to, or blamed on, the skyscraper. UK guidance describes including directly relevant committed development where there is a reasonable degree of certainty that it will proceed. UK guidance on committed development
Estimate how people will travel to and from the building
Estimate demand by building use, time period, and travel mode using methods accepted by the local jurisdiction and evidence appropriate to the site. Show assumptions for occupancy, trip generation, destinations, route assignment, parking, transit access, deliveries, and curb activity where relevant. Separate person trips from vehicle trips: the number of people making journeys and the number arriving in cars answer different questions.
Mixed-use buildings may generate trips that stay within the site, such as a resident visiting an on-site shop, reducing some external vehicle movements. Location also matters: an infill tower with nearby destinations and transit access should not automatically be assigned the same travel patterns as a development at the urban edge. Raleigh’s guidance discusses internal capture and urban context as local-method considerations; its rates and procedures should not be transferred to another city without local approval. City of Raleigh traffic study guidance
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Compare the project case across the whole network
For each agreed analysis period and forecast year, compare the future background case with a future case that includes the tower. Report the incremental effects attributable to the project as well as the total conditions people will experience. Examine more than car delay:
- Roads and intersections: assess operations, queues, delay, site-driveway interactions, and whether traffic can enter or leave the site safely.
- Transit: estimate added passenger demand against available service and capacity where data exist; assess access to stops or stations and conflicts with loading or curb activity.
- Walking and cycling: examine route continuity, crossings, site connections, and points where people walking or cycling may conflict with vehicles.
- Parking and the curb: assess parking demand, loading, deliveries, pick-up and drop-off, and how these uses affect street operations and access.
- Safety: consider relevant safety conditions and how proposed access arrangements change exposure or conflicts.
Use locally accepted level-of-service or quality-of-service methods rather than assuming one metric applies everywhere. Professional practice has increasingly emphasized safety, mobility, and access for all modes instead of vehicle operations alone. The Institute of Transportation Engineers’ multimodal transportation impact analysis guidance describes this broader approach. Its detailed Recommended Practice is listed by TRID as publication RP-020G-E, ISBN 9781737766100, published in January 2023. TRID publication record
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Separate existing problems from project effects, then match mitigation
A crowded intersection or full train may be an existing or background problem. The assessment should show what changes because of the tower, rather than attributing every future difficulty to the project. Conversely, a modest citywide traffic change does not rule out a meaningful localized effect at a driveway, crossing, stop, or intersection.
For each identified project-related effect, connect mitigation to the demand or access issue it addresses. Depending on local rules and evidence, measures may include:
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- Revising site layout, driveway location, or access arrangements.
- Improving pedestrian or bicycle links and crossings.
- Improving access to transit or coordinating service measures.
- Using travel-demand management to encourage alternatives to driving.
- Making a targeted roadway or intersection improvement.
Compare mitigation alternatives using consistent assumptions. Useful comparison measures include person and vehicle trips by period, transit demand and access, intersection delay and queues, safety, walking and cycling connectivity, parking and loading demand, the project-attributable change, and each measure’s cost, feasibility, timing, responsibility, and expected performance. The appropriate package and who pays for it depend on local law and the evidence. Transport for NSW says development mitigation should be relevant and reasonable, feasible, and practical. Transport for NSW Guide to Transport Impact Assessment, Version 1.1, 2025 print version.
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Forecasts are estimates to test, not outcomes to assume. A travel plan can specify a baseline, measurable targets, who will collect data, how often monitoring will happen, how long it will continue, and what action follows if results differ from forecasts. Potential indicators include vehicle entries, mode share, queues or delay at critical intersections, transit passenger loads where data are available, and observations of pedestrian and bicycle access or safety. Agree the measures locally; they are examples, not a standard checklist.
UK guidance calls for a clear baseline and targets, agreed monitoring duration and frequency, and assigned responsibility. It says monitoring should continue until evidence shows targets have been met consistently. UK guidance on Travel Plans and monitoring
Apply local rules rather than a universal skyscraper threshold
Requirements differ by jurisdiction, and a professional manual or another city’s checklist is not automatically binding at the project site. For example, Raleigh’s traffic studies page, updated July 27, 2026, describes its own review process and criteria. Its administrative details and any cited NCDOT trigger should be checked with the city and NCDOT for current applicability rather than treated as general thresholds. Raleigh traffic studies
For a project-specific assessment, identify the governing planning authority and road and transit operators first. Their agreed scope, accepted methods, local data, and review requirements determine how to assess the tower’s effects; no single trip rate, congestion trigger, or mitigation package applies to every skyscraper.
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