As per above the cost per passenger mile on a tram is almost half that of a bus in the US – likely the same in the  UK

The features  below  mean trams offer a higher quality of service (reliability, frequency, smoothness, comfort, speed), not forced to sit close to strangers) than buses and so attract 25% of passengers from cars, which buses do not:

• Shorter service intervals than buses- 6- 10 minutes around the day – “turn up and go” service
• Very rapid boarding and deboarding (leads to faster service, shorter intervals) – worth investing in off tram ticketing due to much higher passenger volumes
• Attract car drivers to the tram and trams can have green wave, buses meaning the tram is not delayed by traffic unlike buses
• Plenty of room so you are never left behind (also due to higher service frequency)
• Spacious – passengers are not crammed next to others in parallel rows of bench seats, staring at the back of passengers’ heads
• You will not be trapped in a bench seat next to a stranger (children and young women)
• per passenger mile cost is cheaper (not necessarily reflected in fare structure as on trams people are prepared to pay more for better service)
• Smoother ride, more comfortable – passengers stand near doors for rapid boarding and de-boarding
• Fixed routes, cannot be suddenly abandoned or suddenly changed and this encourages office and house developers to build alongside, which is not the case with buses

The above features all stem from the fundamental technical and economic differences between a bus and a tram – expanded below:

Summary of engineering issues:

There are intrinsic inescapable differences between a rail vehicle and an automotive type vehicle such as a bus. The bus has to have steering, and suspension, and be light enough so it can steer and stop, and these factors limit its size, the seating arrangement and crucially the door numbers and sizes. On a bus, the doors have to be smaller to make room for all the other automotive parts, whereas a larger tram without road large wheels, steering, suspension etc in the way can have more doors and they can be much larger.

Furthermore, compared to a double-deck bus, a two-car tram effectively has two doors for what was the upstairs of a bus, whereas on a double-decker passengers have to negotiate not only the stairs but other exiting passengers from the lower deck through its smaller doors.

Because trams are not jerky and accelerate smoothly passengers can stand up and move to the large doors as their stop approaches (just like on the underground). This all leads to trams having a boarding and de-boarding time of about 20 secs whereas on a bus this can be up to 2.5 minutes.

Being larger, trams can have a few rows of parallel same-facing forward bench seats, lots of standing room and are jerk-free enough for passengers to be comfortable standing and moving around whilst in motion, and can walk towards the doors as their stop approaches (speeding de-boarding). In contrast, buses have to cram people together and are too violent in movement to permit standing comfortably (slowing de-boarding). Single inwards facing seats avoid being trapped as per a bench seat on a bus.

Because a bus can carry fewer passengers per driver the running cost per passenger km is higher than a tram (fewer passengers to share the costs among), so passengers are forced to wait longer and to build up at the stop. Also, bus operators tend to provide service for shorter periods of the day due to the need to keep costs down and cut out the uneconomic times.

Because it has to be lightweight (to stop, start, steer)  a bus also makes a rattley and noisy vehicle. Trams are much heavier and quieter.

Trams also benefit from Green Wave Traffic Light Preemption which “magically” permits them to move through traffic without needing a separate segregated lane.  For non-obvious reasons buses cannot generally have this applied. See a video of a tram in the middle of Brussels leading in a platoon of cars. Note, having the tram there does not slow the cars, as say 300 people on a tram, up to 30% could have been car drivers, which means in fact that 100 cars or so could have been taken off the road, meaning the remaining essential, or through choice drivers get a faster drive.  On the other hand, many bus lanes are taken out due to complaints from car drivers who get discomfited by seeing almost empty buses passing them. See this also for Green Wave

This and other engineering facts lead to trams being faster, more reliable and able to carry 5 times as many passengers per hour as a competing bus line.  This all makes a tram more attractive to drivers than a bus and therefore it is proven that many car drivers will leave their car behind and take a tram – up to 30%.   This in turn leaves the road freer for the tram ( and the essential, car preferring drivers to move faster). So car drivers, perhaps counterintuitively are not delayed by the presence of a tram system – quite the reverse.

Why Trams Work Integrated With Buses, Whereas Buses Alone Don’t, In Tackling Pollution Congestion, Climate Emergency

• Nowhere have buses achieved a significant modal shift from cars to buses because, for the reasons below, they cannot offer the same high quality and prestigious service which a tram can.
• Trams typically get a 30 – 40 % modal shift due to fundamental engineering differences which translate into a more economical and attractive vehicle and service.
• All 7 new trams in Britain have achieved a significant reduction in pollution and congestion, something not achieved with buses alone, but which are great for rural routes or tram feeders, less dense city routes.

https://bathtrams.uk/evidence-that-car-drivers-will-switch-to-trams-but-not-buses-1/

• In trams, passengers are not cramped in bench seats. Passengers are not stuck next to a potential bad actor (important for school children and young women for example) due to non-bench seats and walk-through vehicles.
• Trams are smoother and quieter than a bus due to the rails, whereas a bus has to deal with defects in the road and on a dedicated busway the vehicles soon create ruts and grooves.
• Trams have a much higher capacity than buses

https://bathtrams.uk/relative-carrying-capacity-cars-buses-trams/

• Lower overall cost – more passengers per driver, lower running cost per passenger, financed at 1 % over 40 yrs lower capex. Buses have higher running costs and higher loan charges due to short life and uncertainty.
• Lower energy consumption due to lower wheel friction

https://bathtrams.uk/solving-baths-traffic/comparative-benefits-trams-vs-buses/

• The above means that trams can operate at a much more rapid frequency around the clock – 2 minutes in Budapest, 6 minutes in UK. Buses can’t do this because they have to accumulate enough passengers at bus stops with long service gaps.
• Trams are much more reliable, and coupled with high frequency e.g 6 minutes in Birmingham eliminates the 1/3 extra morning peak journeys to school by permitting even two tram journeys to school to be feasible because even two tram journeys across the city are fast and RELIABLE.
• Tram can climb all the hills in Bath and the road to Radstock without resorting to racks or cables.
• Any fixed rail link increases property values, and commercial activity and provenly attracts businesses and housing alongside, ephemeral bus services do not.
• Any fixed rail link that starts out rural soon attracts development alongside ( eg Metropolitan line – numerous examples.) and regenerates cities markedly and this case study of the huge benefits to Croydon
• Numerous examples of bus schemes that have not been successful in UK eg Swansea £10m failure https://bathtrams.uk/difficulties-and-problems-encountered-with-bus-rapid-transit-in-the-uk/
• It has been shown that the main reason British cities are less productive than continental ones is the poor public transport ie relying only on buses. https://bathtrams.uk/birmingham-isnt-a-big-city-at-peak-times-how-poor-public-transport-explains-the-uks-productivity-puzzle/

https://bathtrams.uk/buses-and-busways-some-factual-observations-by-prof-lewis-lesley/

• Trams have zero pollution at the point of use or production if run on renewables with very low friction losses so much lower energy consumption. Buses have large tyre, brake and road dust emissions equal to the exhaust emissions. Electric cars are not a solution either due to the tyre and road tar pollution. and the vast demand for rare minerals.
• Trams have much lower bearing pressure and shock loading than buses, and it is buses that are breaking up Bath’s roads and vaults.
• A tram’s inflexibility compared to a bus is in fact an enormous advantage counterintuitively.  

THE FOLLOWING IS AN EXTRACT FROM THE CONFERENCE BROCHURE

The move to zero-carbon and low-particulate transport is now inevitable.

UK Governments of all political persuasions have repeatedly made poor decisions on transport policy based on wrong information propounded by individuals and organisations with vested interests in maintaining the status quo.

The promotion of electric cars and vans for example takes no account of either the need to double electricity generation and the capacity of the distribution cables and national grid within 15 years or the use of finite resources of rare materials such as lithium.

Eminent journalist and writer on transport Christian Wolmar noted that decisions such as the Beeching rail closures, and the promotion of diesel vehicles were later widely discredited and now seem absurd.  They have resulted in congestion and pollution in our cities and atrocious transport infrastructure with which the public has to struggle on a daily basis.

Air pollution much coming from rubber tyre and road surface wear, is thought to cause and contribute to as many as 40,000 premature deaths a year in the UK already, especially among vulnerable people such as those with existing respiratory problems.  But perhaps even worse are the unknown effects on young children, whose lung capacity can be permanently stunted, and their health permanently damaged, by exposure to these pollutants early in life.  In aged school buses air pollution inside is greater than in the air outside.  Not enough has been done to combat the serious damage to human health caused by transport polluting the air.  Research in June 2018 showed it cost the NHS £6bn.

The 8 new trams in Britain have already achieved measurable and significant reduction in pollution and congestion, something buses have never achieved such as the failed Swansea scheme costing £10m, one of many similar failures.

Trams have no rubber tyres meaning zero dangerous rubber tyre dust pollution and driving their wheels requires 85% less energy than do wheels with inflated rubber tyres.