Add a field to the URL file that uses just a single character to represent whether the camera is Fixed or Mobile.
eg:
F=Fixed
M=Mobile

eg: see this header for an example:
POSWGS:S:21|NAME:S:32|VILLAGE:S:24|CITY:S:21|STREE T:S:38|HOUSENUMBER:S:5|PHONE:S:13|bBMW:B:1

the last entry bBMW:B:1 means
b = Byte
BMW = name
B = Boolean (True, False)
1 = length of 1 character

So you could used a name of eg bFIXED:B:1

Then for every speed camera entry in the URL entry you add the field to indicate if it is fixed (T for True) or mobile (F for False).
Then compile the IDX file so it matches.

Then modify the HTM search form to provide the ability to select the camera type you want.

CHECK BOX EXAMPLE
eg: for the above BMW example, I have this code
<TD ALIGN="LEFT">
<INPUT NAME="bBMW_beq" TYPE="CHECKBOX" VALUE="T">
</TD>
<TD></TD>
<TD COLSPAN="3" VALIGN="MIDDLE">
Authorised BMW dealers only
</TD>

So by ticking the box, the search for only finds authorised dealers, which are those with the entry of "T". In this case, T = True, F = False

Adapting the above for my example of TYPE =
<TD ALIGN="LEFT">
<INPUT NAME="bFIXED_beq" TYPE="CHECKBOX" VALUE="T">
</TD>
<TD></TD>
<TD COLSPAN="3" VALIGN="MIDDLE">
Fixed cameras only
</TD>

MENU BOX EXAMPLE
You can do the same with a menu like this
<TD BGCOLOR="#000000" ALIGN="LEFT">
<SELECT NAME="FIXED">
<OPTION VALUE="" SELECTED>Any</OPTION>
<OPTION VALUE=T>Fixed</OPTION>
<OPTION VALUE=F>Mobile</OPTION>
</SELECT>
</TD>
<TD></TD>
<TD COLSPAN=3 VALIGN="MIDDLE">Speed camera type
</TD>

Of course, you can define the character yourself (T or F) to whatever you want
Clear?