The global thresholds InterMapper provides by default are interface errors, short-term packet loss, and response time.

In order to alarm for interface utilitzation, use the SNMP > SNMP High Utilization probe (see attached screenshot), using one instance for each critical interface. They can be added in the Info window for the device, on the Probes tab, using the + button.

The assumption is that critical percentage of utilization for different interfaces of different types will vary and that a single setting wouldn’t necessarily even be valid for all interfaces on a single device.