Table 2 The input variables used in calculations of the pressures. In most cases, there is no data available on uncertainty, and it is based on author judgement (AJ).

Accidents, cases/a [3,24]

The number of injuries and deaths in traffic accidents in the Helsinki metropolitan area. Poisson distribution is used to describe the uncertainty.

Injuries: Poisson(1129)

Deaths: Poisson(26)

Accident costs, €/d [24,25]

The societal costs of traffic accidents were 227 million euro in Helsinki in 2004. The numbers are scaled up from Helsinki to the metropolitan area based on the numbers of people injured in accidents. The uncertainty is based on the standard deviation of the variable Accidents (deaths), which is ca. 20% of the mean.

We assume that half of the accidents are attributable to private car traffic, while the other half is attributable to other traffic modes (walking, cycling, public transportation). In addition, the accident risk is proportional to the change in traffic volume, but there is uncertainty about the slope. The expected value is that when traffic volume decreases by 10%, accident risk decreases by 5%; but it could vary between 0% and 10% (the latter being the default assumption in the guidelines for road construction planning).

var a:= 227 M*((1129)/724)/365; a:= normal(a,a/5)

var b:= vehicle_km; b:= (1-b/b[comp_fr=0])*triangular(0,0.5,1); b:= (1-b)*a*0.5*vehicle_km

Vehicle price, €/vehicle [26]

Price of a new vehicle. Note that the interpretation is slightly different with different vehicles. The car price is the price that a random new car would cost, and it has therefore large uncertainty. The price of a composite vehicle is the average price of a taxi-style car in Finland, and the confidence intervals are narrower because there is no individual uncertainty. This is because the price of an individual car affects the costs of individual car trips, while the cost of a composite trip is dependent on the total cost of the fleet to the service provider. The same typical vehicles are used as in the Emission factor.

8-seat vehicle: 39520*Triangular(0.75,1,1.25)

4-seat vehicle: 22600*Triangular(0.75,1,1.25)

personal car: lognormal(19100,1.5)

[median, geometric standard deviation for lognormal distribution]

Vehicle lifetime, a Author judgement (AJ)

Expected operation time of a new vehicle.

8-seat vehicle: 7*Triangular(0.75,1,1.25)

4-seat vehicle: 5*Triangular(0.75,1,1.25)

personal car: 9*Triangular(0.7,1,1.3)

Cap variab, fraction (AJ)

The value a car-owner gives to capital costs of the car as a fraction of the true costs. Each row represents one possibility for the distribution of individual valuations in the population. Probability distributions are used to represent this variation within the population.

Three possible distributions of variation within the population:

A: Uniform(0,1)

B: Triangular(0,0,1)

C: Bernoulli(0.2))

Cap uncert, – (AJ)

The uncertainty between several valuation distributions about Cap variab on the population level.

A: 1/3

B: 1/3

C: 1/3

Trips per car, trips/d/car (AJ)

Average number of trips per car per day, i.e. the cumulative number of passengers that use the car during the day. This value is used to calculate the vehicle capital costs.

uniform(4,10)

Parking space, €/d/parking space [25]

Cost of a parking space to society due to the loss of the land, and maintenance costs. The average price of development land in Helsinki is around 300 €/m², and one parking space requires ca. 20 m². The standard values in road planning are 30 years for scope and 5%/a for discount. Opportunity cost for land is calculated based on these values; in addition, it is assumed that 50% of composite traffic parking places can be located in areas where the parking cost is negligible.

9.1*lognormal(1,1.3)

Parking price, €/trip [27]

The cost of 30 min parking in zones 1, 2, 3 in Helsinki. It is assumed that each car trip involves 30 min of parking during daytime, while during evening and night, the parking is free. Also daytime parking at home is included in these estimates, although it is difficult to price. In any case, it is common to pay at least 5–10 euro per month for a parking place (or more for a garage), which is 15–30 cents per day. Due to the uncertainties, the confidence intervals are large.

Downtown: 2.4*0.5*Triangular(0,1,2)

Other centre: 1.2*0.5*Triangular(0,1,2)

Suburb: 0.6*0.5*Triangular(0,1,2)

Emission factor, g/km [26,28]

Fine particle and carbon dioxide unit emissions for average vehicles. Fine particle emissions are taken from the Lipasto model using average (mixed gasoline and diesel) values for personal car and diesel EURO3 (applied since 2000) values for composite vehicles. For CO₂, typical emissions of a new car were used based on the Finnish Vehicle Administration AKE. The following vehicles are used as typical examples of the class:

8-seat vehicle: Toyota Hiace 2.5 D4D 100 4 door long DX bus (diesel)

4-seat vehicle: Toyota Corolla 2.0 90 D4D Linea Terra 5 door Hatchback (diesel)

Car: Toyota Corolla 1.6 VVT-i Linea Terra 5 door Hatchback (gasoline)

var a:= triangular(0.3,1,1.7)

var b:= triangular(0.9,1,1.1)

PM emission:

8-seat vehicle: 0.1*a

4-seat vehice: 0.1*a

personal car: 0.047*triangular(0,1,2)

CO2 emission:

8-seat vehicle: 232*b

4-seat vehicle: 153*b

personal car: 168*triangular(0.3,1,1.7)

PM unit lethality, deaths/kg [2]

Primary fine particle emissions of 24290 kg/a caused 12.5 deaths in a risk assessment study in Helsinki (Tainio et al 2005). We use the distribution of deaths per emission derived from that study.

fractiles([-722.3, 5.640, 42.28, 59.87, 80.13, 115.0, 203.7, 293.9, 359.8, 413.2, 464.0, 513.9, 566.2, 623.3, 685.4, 757.7, 844.1, 951.9, 1093, 1314, 2805])/1 M

Emission unit cost, €/kg [1,2,25]

The value of a statistical life is 0.98 – 2 M€ (Watkiss et al. 2005). CO₂ emission trade started in the EU this year, and the market price is used. According to newspapers Helsingin Sanomat (May 7, 2005) and Taloussanomat (July 11, 2005), the price has varied between 10 and 30 €/ton. The standard road planning value for CO2 emission is 32 €/ton.

PM emission cost:

PM_unit_lethality*uniform(0.98 M,2 M)

CO2 emission cost:

uniform(5,40)/1000

Driver salary, €/h [29] Statistics Finland 2005

Monthly salary and social security costs (35%), and scaled to one hour assuming 160 hours of work per month. The salary is based on that of bus drivers in municipality-owned bus companies.

var a:= 2313/160*1.35; normal(a,a*0.18)

Fuel consumption, l/km [26]

Fuel consumption of a vehicle. It is assumed that composite vehicles use diesel fuel and cars use gasoline. The values are based on standardised European consumption values of a new car. The same typical vehicles are used as in the Emission factor.

8-seat vehicle: (8.7/100)*Triangular(0.75,1,1.25)

4-seat vehicle: (5.7/100)*Triangular(0.75,1,1.25)

personal car: (8/100)*Triangular(0.5,1,1.5)

Fuel price, €/l (AJ)

Diesel fuel price for composite vehicles; gasoline price for cars. The values are based on a general follow-up of retail prices in Finland in fall 2004 – summer 2005.

diesel: 0.95*triangular(0.8,1,1.2)

gasoline: 1.22*triangular(0.8,1,1.2)

Car maintenance, €/km [30]

Maintenance costs (service, tyres, oil etc.). This is based on Autoliitto's report 'Costs of car 2004'. Insurance and use tax are excluded. Similar to capital costs, there may be other reasons to own the car, and then these would be sunken costs. Original values (assuming an old car with the original price 20000 e, 20000 km/a of driving) (€/a): Maintenance 844 Tyres 320. Thus, 1164/20000 = 0.0582 €/km

Triangular(0.03, 0.058, 0.086)

Ticket, €/trip (AJ)

The income that the service provider wants to receive from composite traffic users in addition to the price of the direct costs (vehicle, fuel, driver, and parking costs).

uniform(0.2,0.4)

Rush delay h/trip, fraction (AJ)

Delay that is caused by increased link intensity. The node contains two values. Delay is the average time of delay due to traffic jams during daytime. Reduction is the relative reduction to 'Link intensity' (average vehicle flow on the 30 most busy roads at 8.00–9.00 AM) that is needed to reduce the delay to 0 min.

Delay: Uniform(0,10)/60

Reduction: 0.3

Time unit cost, €/h [25]

The cost of time spent waiting for a composite vehicle or in traffic jam. This is based on the standard road planning values.

Triangular(0,5.9,11.8)

Drive variab, fraction (AJ)

Willingness to drive. This is expressed as fraction of composite driver's salary. Each row represents one possibility for the distribution of individual valuations in the population. Probability distributions are used to represent this variation within the population.

Three possible distributions of variation within the population:

A: Uniform(-0.3,0)

B: Triangular(-0.1,0,0.3)

C: Uniform(-0.2,0.2)

Drive uncert, – (AJ)

The uncertainty between several valuation distributions about Drive_variab on the population level.

A: 1/3

B: 1/3

C: 1/3

Car occupancy, fraction [31]

Proportion of cars with different numbers of passengers. The original data is from streets entering downtown Helsinki during one weekday (from 6.00 to 21.00) in May.

Passengers (incl driver):

1: 0.72

2: 0.233

3: 0.033

4: 0.01

5: 0.004