1 Briefing notes why trams (with buses) work in cities better than buses only

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Links to other memoranda in this series:

 

  1. ComparativeBenefits of Trams and Buses in Urban Public Transport
  2. Dispelling the myth that trams need special seperate segregated path through traffic
  3. “Glue-in-the-Road” TramTrack Systems versus Conventional Deep Excavation Methods
  4. Why trams are essential to improve city productivity
  5. Overhead wire-freeTechnologies for Tram Propulsion
  6. Birmingham Tramworks Show Utilities Don’t Always Need to Be Moved: Minimal-Dig Track Methods in Action – A UK & International Perspective

Technical Memorandum 1: Benefits of Trams in Conjunction with Buses, Rail, and Modern Surface Track Technologies

Subject: Comparative Benefits of Trams and Buses in Urban Public Transport
Prepared for: Policy Makers and Infrastructure Planners
Prepared by: Bristol and Bath Tram Association / West of England Transport Association
Date: June 2025

  1. Introduction

Two key innovations differentiate and improve modern tram systems. One is the ability to run through traffic unimpeded on shared paths due to advanced traffic light control, and the second is the use of rapidly installable track on the surface that does not require deep excavation or the wholesale diversion of buried services.

Trams, or light rail, are often mistakenly perceived as merely expensive, inflexible buses. However, when deployed on appropriate corridors, they significantly enhance urban worker productivity and the entire city economy compared to bus-only or car-dominated transport systems. Furthermore, modern track-laying methods dramatically cut installation times and disturbance along the route.

Trams enable affordable and reliable travel from greater distances than buses or cars, thereby expanding the labour pool for employers and attracting higher-value investment into the city. This ultimately boosts productivity and the local economy [5, 6]. Crucially, the economic improvements generated by such investments often lead to a positive return on investment, effectively offsetting the cost of borrowing. For example, the Edinburgh tram project’s economic justification was strong: Phase 1a (Airport to Leith Waterfront) estimated a Benefit-Cost Ratio (BCR) of 1.77, meaning £1.77 was returned for every £1 invested. When Phase 1b was included, utilizing more efficient track methods, the BCR improved to 2.31, indicating a robust economic justification compared to other rail projects [35]. Appropriate corridors should be identified through impartial, evidence-based cost-benefit analysis.

  1. Key Advantages of Modern Tram Systems

Many policymakers and the public are unaware of two critical advantages that significantly differentiate trams from buses: Green Wave Traffic Signal Pre-emption (GWTP), and modern track installation systems that make deployment significantly cheaper and faster.

2.1 Green Wave Traffic Signal Pre-emption (GWTP)
GWTP is far more advanced than simple signal priority (SP) often used for buses, which only acts on a light-by-light basis and still leaves buses vulnerable to traffic congestion. GWTP coordinates all traffic signals along a corridor in advance of the tram to create continuous “green waves.”

  • Coordinated Traffic Flow: GWTP coordinates all traffic signals along a corridor to ensure trams experience a continuous “green wave,” allowing them to glide through traffic and intersections without delay.
  • Intersection Clearance: Side roads are briefly held at red lights just ahead of the tram to prevent route blockage, meaning the tram driver rarely encounters traffic directly in front of them.
  • Unimpeded Movement: This enables trams to pass through intersections without stopping, effectively creating the impression that other traffic is not present.
  • Reduced Segregation Needs: It significantly reduces the need for costly and space-consuming full segregation from other vehicles.
  • Improved General Traffic Efficiency: Remaining motorists benefit from smoother signal coordination, improving overall traffic flow.
  • Limited Bus Application: Buses can only benefit from local signal priority (SP), which lacks corridor-wide integration and is far less effective [18].
  • Predictable Service: GWTP ensures highly predictable service patterns, increasing public confidence and ridership (e.g., “you can set your watch by the tram arrival in Geneva”).
  • Global Recognition: Generally, this sophisticated system cannot be applied to buses due to their flexible routing and stopping patterns (refer to World Bank references).

(See also Technical Memorandum 2 for full detail.)

2.2 Embedded Track Technologies
Traditional tram installation methods often required extensive excavation and total service diversion, leading to months of disruption and slow progress (as seen in the initial Edinburgh tram project, which faced delays and budget overruns primarily due to the use of an expensive deep-dig track system requiring total service diversion). Modern methods significantly mitigate these issues.

Modern Embedded Track / Slab / Waybeam / Glue-in-Road Track Technology offers:

  • Rapid Installation: Enables quick installation directly into the road surface with minimal disruption to streets and businesses.
  • Reduced Disruption: Avoids extensive service diversions commonly associated with traditional construction. Modern methods allow tracks to be laid over existing services while still enabling rapid access when needed.
  • Cost Savings: Reduces installation costs by up to 50% compared to conventional deep excavation methods [15, 16].
  • Faster Completion:
    • Traditional method: 6–12 months per kilometer with major road and business disruption.
    • Modern method: 2–3 months per kilometer with reduced excavation and swift restoration, with some systems offering rapid installation rates of tens of meters per week.

(See Technical Memorandum 3 for comparison of installation methods.)

  1. Core Benefits of Trams Over Buses

3.1 Operational and User Benefits

  • Passenger Capacity & Labour Efficiency:
    • Trams can carry up to 450 passengers per vehicle versus approximately 90 on a typical bus.
    • A tram route can transport 4–5 times more passengers per hour than a comparable bus route [20].
    • Results in a lower driver cost per rider, which is vital amid current driver shortages.
  • Passenger Boarding & Time Savings:
    • Trams average approximately 20 seconds per stop.
    • Buses typically require 2–3 minutes per stop.
    • Level boarding and wide doors enable all-door, fast boarding.
  • Passenger Comfort & Safety:
    • A smooth, electric ride allows safe movement within the vehicle and rapid deboarding [19].
    • Spacious interiors with fewer obstructions are preferred by women, children, and groups.
    • Quiet operation enhances urban liveability [23].
  • High User Appeal & Modal Shift:
    • Up to one-third of tram users previously drove private cars [7].
    • Trams are viewed as high-quality, clean, and permanent public transport [13].
    • Modal shift helps reduce urban congestion [24].
  • Service Quality:
    • Reliable frequency reduces reliance on strict timetables.
    • Consistent journey times maintained thanks to GWTP.
    • Extended service hours improve accessibility.
  • Vehicle Longevity:
    • Trams last 30–50 years.
    • Buses typically last 12–15 years.
    • Fewer replacements reduce lifecycle costs [22].
  • Environmental Performance:
    • Zero local emissions improve air quality [25].
    • Less microplastic and brake dust pollution [26].

3.2 Infrastructure and Economic Benefits

  • Catalyst for Development: Encourages high-density housing, retail, and job creation [27].
  • Improves Regional Productivity: Expands labour catchment area and attracts investment [5].
  • Lower Operating Cost per Rider: Higher capacity and GWTP improve economics [20].
  • Automation-Ready: Fixed guideways enable future autonomous operations.
  • Supports Place-Making & Urban Quality: Enhances public spaces [28].
  • Enables Car-Free Lifestyles: Improves reliability, reducing car dependence [29].

(Further elaborated in Technical Memorandum 4.)

  1. Limitations of Bus-Only Systems
  • Higher operating costs due to more drivers per passenger and shorter lifespan.
  • Reduced off-peak frequency [30].
  • Susceptible to traffic delays and obstructions.
  • Less appealing to “choice” users.
  • Perceived as noisy due to the flimsy construction of the automotive vehicle and uncomfortable due to the need to closely pack users.
  • Uncertainty in routing discourages development.
  • Greater environmental impact [26].

Of course, a viable bus network is also essential to complement the tram network for less travelled routes, but will not work on its own.

  1. The Case for Integration

Trams and buses are complementary, not competitors.

  • Trams: Best for high-demand, high-capacity corridors.
  • Buses: Provide flexible coverage and feeder services.

An integrated network maximizes mobility, coverage, and system resilience [31].

 

  1. References

[1] Transport for London, “Green Wave Traffic Management,” 2022.
[2] European Tram Network Association, “Benefits of Signal Priority for Trams,” 2021.
[3] UITP, “Modal Shift and Public Transport Attractiveness,” 2020.
[4] PTEG, “Car Users Switching to Tram Services,” 2019.
[5] OECD, “Urban Productivity and Public Transport,” 2021.
[6] World Bank, “Transport and Economic Development,” 2020.
[7] ITF, “Tram Passenger Modal Shift Analysis,” 2018.
[8] National Transport Authority, “Bus Passenger Car Use Conversion,” 2019.
[9] European Commission, “Integrated Public Transport Systems,” 2020.
[10] City of Zurich, “Tram and Bus Network Efficiency,” 2019.
[11] Urban Land Institute, “Fixed Transit Lines and Development,” 2018.
[12] RICS, “Land Use Planning and Tramways,” 2020.
[13] Sustrans, “Permanent Infrastructure and Modal Shift,” 2021.
[14] Metro Magazine, “Trams vs Buses: Cost and Reliability,” 2019.
[15] UK Tramway Association, “Modern Embedded Track Installation,” 2022.
[16] City of Portland Transport Dept., “Track Installation Times and Costs,” 2021.
[17] Transport Research Lab, “GWTP Effects on Traffic Flow,” 2020.
[18] National Bus Operators Association, “Signal Priority for Buses,” 2019.
[19] Transport Safety Board, “Passenger Movement and Vehicle Motion,” 2022.
[20] Transit Capacity Benchmarking Report, 2021.
[21] Driver Retention Study, Urban Transport Institute, 2020.
[22] Vehicle Lifespan Analysis, National Transport Safety Board, 2019.
[23] Environmental Transport Journal, “Noise Pollution and Comfort,” 2021.
[24] Bath Trams Report, “Street Running and Congestion,” 2022.
[25] International Energy Agency, “Electric Public Transport Emissions,” 2021.
[26] Environmental Protection Agency, “Microplastic Pollution from Transport,” 2020.
[27] City Development Quarterly, “Regeneration and Public Transport,” 2019.
[28] Urban Design Review, “Placemaking and Transport,” 2021.
[29] Transport and Society Journal, “Car-Free Lifestyle Study,” 2020.
[30] National Transport Commission, “Bus Service Frequency Report,” 2019.
[31] Public Transport Research Group, “Integrated Network Strategies,” 2022.
[32] TriMet, “Transit Signal Priority Evaluation,” Portland, 2006. https://trimet.org/pdfs/publications/transit-signal-priority.pdf
[33] Wikipedia, “Sydney Coordinated Adaptive Traffic System.” https://en.wikipedia.org/wiki/Sydney_Coordinated_Adaptive_Traffic_System
[34] Wikipedia, “King Street Transit Priority Corridor.” https://en.wikipedia.org/wiki/King_Street_Transit_Priority_Corridor
[35] City of Edinburgh Council, “Steer Report – Business Case for Edinburgh Trams to Newhaven,” 2020. https://www.edinburgh.gov.uk/tramstonewhaven/downloads/file/68/steer-report

 

Links to other memoranda in this series:

  1. ComparativeBenefits of Trams and Buses in Urban Public Transport
  2. Dispelling the myth that trams need special seperate segregated path through traffic
  3. “Glue-in-the-Road” TramTrack Systems versus Conventional Deep Excavation Methods
  4. Why trams are essential to improve city productivity
  5. Overhead wire-freeTechnologies for Tram Propulsion
  6. Birmingham Tramworks Show Utilities Don’t Always Need to Be Moved: Minimal-Dig Track Methods in Action – A UK & International Perspective

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