Problem Assumptions

5. 2 Problem Assumptions

The assumptions made in developing the train slot generation model, simulation platform, and related solution techniques are provided in this section. Such assumptions are necessary when relevant data is unavailable or to create mathematically tractable problem formulations.

1. Train slot definition

A train slot is defined as the use of a route from shipment origin to shipment destination during a given period of time. For simplicity, we will assume that the owner of the train slot has the right to operate along the route for the given train slot every week day for a season.

European Commission UMD and UOB Sixth Framework Programme

Organization Code:

2. Passenger traffic has priority in the REORIENT corridor In practice, passenger traffic has priority over freight traffic. Thus, the freight train

timetable should be constructed based on the residual track capacity given existing passenger traffic. It was difficult to obtain passenger train timetables for the entire REORIENT corridor. Based on empirical knowledge, it was assumed that the freight traffic can only be scheduled at night (i.e. from 22:00 to 5:00) from Monday to Friday.

3. Train speed The train speed is dependent on the track segment. Different speed limits are

designated for different track segments within the REORIENT corridor. In practice, however, the train does not travel at full speed. Thus, it is assumed that the train will travel at an average speed along the track. The speeds range from 30 km/hr to 120 km/hr. However, on the majority of tracks, average speeds are between 60 km/hr and 80 km/hr.

4. The zone-to-zone O-D demand table is given

Demand for transport by railcar through the REORIENT corridor has been obtained through the demand model described in Section 2.2. Thus, shipments are generated from a known, fixed, and deterministic demand generation distribution.

5. Classification and train make-up policies are assumed

A first-come, first-serve policy for classifying and train make-up planning is assumed in this work.

Organization Code:

UMD and UOB

European Commission

Classification:

Unclassidied

Sixth Framework Programme

6. Delay is incurred at the intermodal terminals, classification yards or border crossings

In the simulation platform, it is assumed that the service times at the intermodal terminals, classification yards and ports are random variables. Service times at the terminals, ports and classification yards are a function of queues that form at these facilities and are assumed to be uniformly distributed over a range of times that depend on the type of mode-to-mode connection, whether or not the shipments involved are containerized or bulk, and expert information. Delays at border stations experienced by trains are a function of assumptions concerning the condition of the infrastructure, existing technologies and pre-existing agreements,

i.e. the level to which the border crossing operations are streamlined. The average time required under current and improved operating conditions is employed in this work and is based on observational data and expert information.

7. Rolling stock issues (equipment availability)

The empty car distribution problem is not considered. Thus, rolling stock (e.g. locomotives and railcars) is assumed to be always available when required. Actual train length and axle load limitations were employed when available and were estimated otherwise. When estimated, a constant value is assumed within a given country along the corridor.

European Commission UMD and UOB Sixth Framework Programme

Organization Code:

8. Operating cost assumptions Fixed seasonal operating costs are assumed. The operating costs are composed of the

infrastructure cost, the locomotive cost, and the track access cost. The operating cost is country specific.

9. Cyclic portion of the path is allowed

In some instances, cycles may exist in the trains path. This is due to the fact that some classification yards are not directly on the REOREINT corridor. Trains that are served by such classification yards must take a detour and return to the main corridor. These detours result in routes with small cycles.