When defending a motorist with a disability, counsel should consider whether or not the results of some or all of the field sobriety tests should be excluded for failure to comply with the American with Disabilities Act (ADA) of 1990.  The ADA states in relevant part:
No qualified individual with a disability shall, by reason of such disability, be excluded from participation in or be denied the benefits of the services, programs or activities of a public entity, or be subjected to discrimination by any such entity. 
A “public entity” is broadly defined under the statute as “any State or local government” and “any department, agency, special purpose district, r other instrumentality of a State or States or local government.  In order to litigate a motion to suppress under this argument, the motorist must establish that: (1) they have a qualifying disability; (2) the arresting department must be a “public entity” to which the act applies, and; (3) the driver must have been discriminated against either by a policy of discrimination, or by deliberate indifference to the driver's disability.
In evaluating this argument, counsel should evaluate whether or not the client's disability precluded the field sobriety tests from being administered or evaluated in a non-discriminatory manner. If so, then the arresting officer is required to make reasonable accommodations, which might, for examples, include offering different tests that the motorist might reasonably be expected to “pass” if they were not disabled. 
This argument was successful in the instance where a hearing impaired driver was asked to undergo field sobriety testing after being involved in a car accident. Although the driver was able to understand some of the demonstrations, his inability to read lips made it impossible to understand what was required of him. After failing the FSTs the driver was arrested and jailed for two days, until the blood test came back demonstrating that he was not impaired. A successful suit brought about a $230,000 judgment, which was upheld on appeal. 
Interestingly, a study conducted to investigate this problem showed that only 53% of all officers surveyed had encountered this problem. Even more amazing is that 86% of them reported being able to complete the FSTs.  A variety of means were identified to overcome the verbal barrier, the most commonly cited being the use of handwritten instructions and/or the use of hand
gestures.  At least 53% of the officers surveyed believed that the driver was able to read their lips in order to understand the instructions.  Also of interest, only 42% of the officers surveyed even knew how to contact a interpreter for the deaf. 
 42 U.S.C. 12101.
 42 U.S.C. 12132.
 42 U.S.C. 12131(1)(A)(8)
 For example, saying the alphabet, using the finger dexterity test or a counting exercise.
 See Delano-Pyle v. Victoria County, Texas, 302 F.3d 567 (5th Cir 2002).
 Franklin, R, IMPEDIMENTS TO TESTING: THE IMPACT AND LANGUAGE BARRIERS ON THE FIELD SOBRIETY TESTING FUNCTION. Nat'l Sobriety Testing Resource Center, (Sept. 2005), DTNH-22-02-G-05025.
 Id. at 11.