RealAge reports all the symptoms of the common cold contribute to slow reaction times, fatigue, and general unsteadiness. With puffy, watering eyes, vision is also said to be impaired, giving you the characteristics of being mildly drunk.
It says sneezing usually lasts around 2-3 seconds, so at 110km/h on the freeway, just one sneeze is effectively like driving up to 91 metres with your eyes closed. If you have a bad cold, repetitive sneezing can be even more hazardous.
On top of this, the report says driving while suffering from a cold can be made more dangerous if you have taken medication. Most cold and flu medicines contain a decongestant, which can cause sleepiness and very relaxed and slow-to-react muscles. A label on the back should advise of possible drowsiness effects, with some warning users not to operate machinery.
The advice is, if you really need to drive while suffering from the sniffles, it's best to check any medication labels, and if possible, not take any medication until you finish your driving. Either that, or simply ask a friend or relative to drive you.