The SLCODE parameter tells the Analyst Drive program to preprocess the screenline files according to the code value. Using this option will create a separate count file for each OD matrix to be estimated, and so the optimization can be performed for a single matrix at a time as opposed to an aggregated estimation. The key benefit of this method is that the estimation should perform better than an aggregate method because there are essentially fewer variables per data point (since we are essentially creating more data points by preprocessing) to be optimized. On the other hand, this method works on the assumption that the volume proportions before and after the estimation should be equal, which may not necessarily be true.

To use the SLCODE parameter, the user must provide an input ICP file for each matrix to be estimated. The SLCODE is a sequence of numbers which tell the program which class matrices/ICPs belong to which screenline. The SLCODE is a sequential series of two number sets. The first set of numbers tell the program the first and last number matrix that the first screenline file corresponds to; the second set of two numbers are the first and last matrix that the second screenline file corresponds to, and so on. Some examples are given below to help show how to determine the SLCODE value.

• SLCODE Example 1 — If we had four matrices to estimate with a single screenline file, then we want four preprocessed screenline files from a single initial screenline file. In this case, the first matrix to be estimated from the first and only screenline file would be 1 and the last matrix to be estimated by it would be 4 and so we arrive at the SLCODE of 14.

• SLCODE Example 2 — If we had five matrices to estimate and two screenline files then our SLCODE value must contain four sequential numbers (two for the first screenline file, two for the second). If the first screenline file corresponded to the 1st, 2nd and 3rd matrices then the first matrix to be estimated using this screenline file is matrix 1 and the last to be estimated using this screenline file is matrix 3 giving 13 for the first two numbers of the SLCODE. The second screenline file corresponds to the 4th and 5th matrices, so the first matrix number to be estimated using the second screenline file is 4 and the last is 5. This gives 45 as the last two numbers of the SLCODE parameter, and so we find the SLCODE value would be 1345.

• SLCODE Example 3 — If we had eight matrices and four screenline files such that the first screenline file corresponded to the 1st matrix then the first and the last matrix to be estimated with the first screenline file is 1, and in this case the two-digit SLCODE portion is given by 11. Now, if the second screenline file corresponded to the 2nd, 3rd, 4th and 5th matrices (25), the third screenline file corresponded to the 6th and 7th matrices (67), and the fourth screenline file corresponded to the 8th matrix (88) then the SLCODE would be 11256788.

The SLCODE parameter can be used to estimate up to nine matrices from a single (or more) count set(s). It cannot be used in conjunction with the ICPARRAY and SLARRAY parameters.